GH-15672: add temp directory removal for tests called and used tempfile.

[wendycwong]

This PR removed all temp files used in python unit test for this issue: #15672

[tomasfryda]

I would probably prefer to modify the test runner a bit instead of making so many changes that won't help in future tests.

I would suggest something like:

def standalone_test(test, init_options={}):
    if not h2o.connection() or not h2o.connection().connected:
        print("Creating connection for test %s" % test.__name__)
        h2o.init(strict_version_check=False, **init_options)
        print("New session: %s" % h2o.connection().session_id)

    h2o.remove_all()

    h2o.log_and_echo("------------------------------------------------------------")
    h2o.log_and_echo("")
    h2o.log_and_echo("STARTING TEST "+test.__name__)
    h2o.log_and_echo("")
    h2o.log_and_echo("------------------------------------------------------------")
    import os
    import tempfile
    with tempfile.TemporaryDirectory() as dir:  # Create a temporary dir that will clean itself
        tempfile._once_lock.acquire()  # Better lock to avoid race conditions (but since we don't test in multiple threads (to avoid side-effects on the backend) it should not matter)
        old_tempdir = tempfile.tempdir
        try:
            tempfile.tempdir = dir  # Tell tempfile to use this temporary dir as the root for all other temporary dirs
            test()
        finally:
            tempfile.tempdir = old_tempdir
            tempfile._once_lock.release()

To test it, you can tell python what should be the default root tempdir by setting TMPDIR environment variable. (But you have to do it before tempdir module is initialized as it reads the value only once).

$ TMPDIR=/my/favorite/dir/ python pyunit_...

NOTE: This should work in python 3.2 and above.