[Lockfile](https://pypi.org/project/lockfile/) has not been maintained
since around 2015. Further, the functionality it provided seems poor - a
review of the code indicated that it used the presence of the PID file
itself as the lock - in Unix, using a file's existence followed by a
creation is not atomic, so a lock could be prone to race conditions.

The lockfile package also did not clean up after itself - a process
which was destroyed unexpectedly would not clear the created locks, so
some faulty logic was added to mainUtils.py, which checked to see if a
process with the same PID as the lockfile's creator was running. This
is obviously failure prone, as a new process might be assigned the same
PID as the old lockfile's owner, without actually being the same process.

(Of note, the SIG_DFL argument to os.kill() is not a signal at all, but
rather of type signal.handler. It appears that the python cast this
handler to the int 0, which, according to man 2 kill, leads to no signal
being sent, but existance and permission checks are still performed. So
it is a happy accident that this code worked at all)

This commit removes lockfile from the codebase entirely.

It also adds a "PIDLockFile" class which provides an atomic-guarenteed
lock via the mkdir and rmdir commands on Unix - thus, it is not safely
portable to Windows, but this should not be an issue as only Unix-based
utilities use the "simple_main()" function.

PIDLockFile provides API compatible classes to replace most of the
functionality from lockfile.PidLockFile, but does remove any timeout
logic as it was not used in any meaningful sense - a hard-coded timeout
of 1 second was used, but an immediate result of if the lock is held is
sufficient.

PIDLockFile also includes appropriate __enter__, __exit__, and __del__
attributes, so that, should we extend this class in the future, with
syntax is functional, and __del__ calls release, so a process reaped
unexpectedly should still clean its own locks as part of the garbage
collection process.
Authored-by: NTyler Ramer <tramer@pivotal.io>

We are renaming the docker images we use with concourse to have the gpdb
version in the actual image name rather than in the tag. The contents of
the images will be the same as before.
Authored-by: NKaren Huddleston <khuddleston@pivotal.io>

Also updated docker README to reference new build image.
Co-authored-by: NDavid Sharp <dsharp@pivotal.io>
Co-authored-by: NKaren Huddleston <khuddleston@pivotal.io>

- Include how to make Greenplum within docker accessible to SQL editors
  running on the local machine (outside of docker).
- Update the pip install command so that psutil and lockfile are
  accessible when the make cluster command is executed.

The centos-gpdb-dev:7 image's bundled gcc versions are now too old
for compiling the gpdb code.

As of this writing, the image pivotaldata/centos-gpdb-dev:7, contains:
- /usr/bin/gcc = 4.8.5
- /opt/gcc-4.4.2/bin/gcc = 4.4.2

pivotaldata/centos-gpdb-dev:7-gcc6.2-llvm3.7 contains:
- /usr/bin/gcc = 4.8.5
- /opt/gcc-6.2.0/bin/gcc = 6.2.0

This commit updates the referenced image in the guide.
Co-authored-by: NKristofer Macoskey <kmacoskey@pivotal.io>
Co-authored-by: NMasashi Dojo <mdojo@users.noreply.github.com>
Co-authored-by: NAmil Khanzada <amilkh@users.noreply.github.com>

- Use the latest gcc (from /opt/gcc_env.sh).
- Add commands to .bash_profile/.bashrc so that stopping and starting the
  container works as expected.
Signed-off-by: NBen Christel <bchristel@pivotal.io>

This guide is based on the centos-gpdb-dev docker images that Concourse uses, thus there are less things we need to add on top.
Signed-off-by: NAmil Khanzada <akhanzada@pivotal.io>