Remove oslo logging from backup unit tests

Remove oslo logging from backup unit tests

Many of the unit tests for backup services import oslo_log and
invoke LOG.debug, LOG.info, etc.  There appears to be no current
reason to do this and, more generally, unit tests for everything
but oslo_log itself should not be doing logging themselves.

This commit removes oslo logging from the backup unit tests.
Closes-bug: 1464772

Change-Id: I2c9f258a43a155e785bac4158cb5e5e0ecfcc797