Add CIMRepository open coverage and align _FormatFilenameAsGlob call sites with its return value

[kev365]

Motivation

CIMRepository is the entry point for reading a WMI CIM repository, and tests/wmi_repository.py
currently carries # TODO: add tests for CIMRepository. This adds that coverage using the
test_data/cim corpus already in the repository.

Adding a test that calls CIMRepository.Open() also exercises the six _FormatFilenameAsGlob()
call sites, which is where the second half of this change applies.

Current behavior (verified, for reference)

_FormatFilenameAsGlob() returns a single string:

        return "".join(glob_parts)

Six call sites take two values from it:

Line	Filename argument
3495	mapping{n}.map
3854	index.btr
3883	(parameter of _OpenMappingFile)
3907	mapping.ver
3928	objects.data
3956	cim.rep

Calling CIMRepository.Open() against test_data/cim at 4917c9b:

ValueError: too many values to unpack (expected 2)
  File "dtformats/wmi_repository.py", line 3883, in _OpenMappingFile
    filename_as_glob, _ = self._FormatFilenameAsGlob(filename)

The existing tests cover IndexBinaryTreeFile, MappingFile and ObjectsDataFile directly, so
this path is not currently reached by the suite.

Proposed change

1. Take the single returned value at the six call sites.
2. Add CIMRepositoryTest.testOpenAndClose, using the existing test_data/cim corpus, resolving
   the existing TODO.

class CIMRepositoryTest(test_lib.BaseTestCase):
    """CIM repository tests."""

    def testOpenAndClose(self):
        """Tests the Open and Close functions."""
        test_directory_path = self._GetTestFilePath(["cim"])
        self._SkipIfPathNotExists(test_directory_path)

        test_repository = wmi_repository.CIMRepository()

        test_repository.Open(test_directory_path)

        try:
            self.assertIsNotNone(test_repository.format_version)
        finally:
            test_repository.Close()

Verification

Re-run from a clean working copy against 4917c9b:

Check	Result
Diff size	6 changed lines in dtformats/wmi_repository.py; 16 added and 1 removed in tests/wmi_repository.py (the removed line is the # TODO: add tests for CIMRepository comment this resolves)
New test, without the call-site change	fails with the ValueError above
New test, with the call-site change	passes
python -m unittest tests.wmi_repository	8 of 8
scripts/wmi_repository.py <repository>	completes; 1,857 lines of output on a format 2.2 repository

Backward compatibility

No format, API, or output change. _FormatFilenameAsGlob() itself is unchanged; only the
call sites and the test module are touched.