Document having clean test run.
* morituri/common/encode.py:
Catch and properly stop on gst.QueryError.
Don't set peak in stop if we had an error.
* morituri/test/test_common_encode.py:
* morituri/test/test_common_renamer.py:
* morituri/test/test_image_cue.py:
Clean up after tests.