Fix typos.
Co-Authored-By: NChristopher Hunt <chrahunt@gmail.com>

Fixes copy-paste issue in `test_pep518_forkbombs`.

It fails if it already satisfies the requirement, when
pip has been modifying via `pip.exe install ...` command.

Fix typos
Use script.pip instead of script.run

Rebased to the latest master
Remove unneeded assertions
Use create_basic_wheel_for_package
Couple other nitpicks

Fix typos and remove unneeded assertions.

Handle the case of invoking pip via pip3 and pip3.7

    ________________ test_constraints_local_editable_install_pep518 ________________
    ...
    ----------------------------- Captured stdout call -----------------------------
    Script result: python -m pip download setuptools wheel -d /tmp/pytest-of-mockbuild/pytest-0/test_constraints_local_editabl0/data/packages
      return code: 1
    -- stderr: --------------------
      Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7fba7fdeb160>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/setuptools/
      Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7fba7fdeb0b8>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/setuptools/
      Retrying (Retry(total=2, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7fba7fdeb4e0>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/setuptools/
      Retrying (Retry(total=1, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7fba7fdeb6d8>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/setuptools/
      Retrying (Retry(total=0, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7fba7fdeb860>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/setuptools/
      Could not find a version that satisfies the requirement setuptools (from versions: )
    No matching distribution found for setuptools

    _____________ test_pep517_wheels_are_not_confused_with_other_files _____________
    ...
    -- stdout: --------------------
    Processing /tmp/pytest-of-mockbuild/pytest-0/test_pep517_wheels_are_not_con0/data/src/withpyproject
      Installing build dependencies: started
      Installing build dependencies: finished with status 'error'
      Complete output from command /tmp/pytest-of-mockbuild/pytest-0/test_pep517_wheels_are_not_con0/workspace/venv/bin/python /builddir/build/BUILDROOT/python-pip-19.0.2-1.fc30.x86_64/usr/lib/python3.7/site-packages/pip install --ignore-installed --no-user --prefix /tmp/pytest-of-mockbuild/pytest-0/test_pep517_wheels_are_not_con0/workspace/tmp/pip-build-env-3un7dqu3/overlay --no-warn-script-location --no-binary :none: --only-binary :none: -i https://pypi.org/simple -- setuptools wheel:
      Collecting setuptools
        Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7fb7cf5a8898>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/setuptools/
        Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7fb7cf5b9588>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/setuptools/
        Retrying (Retry(total=2, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7fb7cf5b9470>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/setuptools/
        Retrying (Retry(total=1, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7fb7cf5b9278>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/setuptools/
        Retrying (Retry(total=0, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7fb7cf5b9208>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/setuptools/
        Could not find a version that satisfies the requirement setuptools (from versions: )
      No matching distribution found for setuptools

    ________________________ test_upgrade_argparse_shadowed ________________________
    ...
    ----------------------------- Captured stdout call -----------------------------
    Script result: python -m pip install argparse==1.3
      return code: 1
    -- stderr: --------------------
      Retrying (Retry(total=4, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7ff07d6db240>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/argparse/
      Retrying (Retry(total=3, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7ff07d6db358>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/argparse/
      Retrying (Retry(total=2, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7ff07d6db400>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/argparse/
      Retrying (Retry(total=1, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7ff07d6db518>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/argparse/
      Retrying (Retry(total=0, connect=None, read=None, redirect=None, status=None)) after connection broken by 'NewConnectionError('<pip._vendor.urllib3.connection.VerifiedHTTPSConnection object at 0x7ff07d6c7710>: Failed to establish a new connection: [Errno -2] Name or service not known')': /simple/argparse/
      Could not find a version that satisfies the requirement argparse==1.3 (from versions: )
    No matching distribution found for argparse==1.3

The main setuptools PEP 517 backend is intended for
explicit usage in `pyproject.toml`, when the project
authors can ensure that their `setup.py` runs without
that directory being implicitly on `sys.path`.

For implicit usage, setuptools now offers a separate
legacy backend that more closely mimics direct
execution of the `setup.py` script.