BUG: MaskOneImageGivenLabelMap test name for baseline comparison.

The test name needs to follow the conventions in the compare_to_baseline
documentation, i.e <example name>Test.

Use a more descriptive name for the second test.

Change-Id: I5e65b9257508a5b86520c7c4b2ab659026d7792d
Merge "BUG: MaskOneImageGivenLabelMap test name for baseline comparison."