Logging audit for trove/guestagent/backup module

Adjust logging to conform to logging standards.
Cleaned up some messages that were unclear. Also
corrected the usage of the word Backup which was
inconsistently capitalized in some messages.

Also addressed a pattern of exception handlers using
LOG.error merely to log the exception (instead of
using LOG.exception)

Change-Id: Id2eb57d3395273f9aebd41de0146f7a2fc2774c8
Partial-Bug: #1324206
Merge "Logging audit for trove/guestagent/backup module"