Activate test_import unit tests with OMERO_USERDIR

[manics]

This is a followup to https://github.com/ome/omero-py/pull/162 (the last ~3~ 4 commits in this PR are new).

1. If OMERO_USERDIR is not set this uses a temporary directory to ensure the unit test does not modify the user's environment since jars are automatically downloaded.
2. Activates all import tests that were previously disabled when OMERODIR wasn't set
3. Fixes broken import tests which apparently were never run in CI
4. Disables the tests activated in step 2 on Windows only since they're failing

Downside of course is that anyone running the full test suite without setting OMERO_USERDIR will end up downloading OMERO.java once (the fixture that sets OMERO_USERDIR to a tempdir is scoped to the session not the function), but I think this is preferable to modifying the default OMERO_USERDIR. Alternatively we could disable the tests by default, but then they'll probably break again.

[snoopycrimecop]

Conflicting PR. Removed from build OMERO-python-superbuild-push#364. See the console output for more details. Possible conflicts:

• PR #228 sbesson 'Add PyYAML as a dependency of omero-py'
  • test/unit/clitest/test_import.py

--conflicts

[manics]

These commits are included in https://github.com/ome/omero-py/pull/162