Don't mix every http request in with the tests output.
Don't print that the file servers are starting unless
-vv flag is passed.

Capture the output of run with run_output which returns
stdout, stderr and exit_code. Test against this rather
than relying on sys.exit.

* use subclass of unittest.TestCase for all test cases

* allow to run single test file (eg. python tools/integration_tests.py)

* test filtering (via --pattern/-p CLI flag)

* use common CLI parser for all tests:
  usage: test.py [-h] [--failfast] [--verbose] [--executable EXECUTABLE]
               [--release] [--pattern PATTERN] [--build-dir BUILD_DIR]

  optional arguments:
  -h, --help            show this help message and exit
  --failfast, -f        Stop on first failure
  --verbose, -v         Verbose output
  --executable EXECUTABLE
                        Use external executable of Deno
  --release             Test against release executable
  --pattern PATTERN, -p PATTERN
                        Run tests that match provided pattern
  --build-dir BUILD_DIR
                        Deno build directory

* respect NO_COLOR variable