Logging audit for guestagent/couchbase

Adjust logging to conform to logging standards.
Cleaned up a few messages that were unclear, and
added some debug messages for recently added
API stubs.

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

Change-Id: I4ed452ddc4e0e9a29f6cbcc9d4e04f3a8b183687
Partial-Bug: #1324206
Merge "Logging audit for guestagent/couchbase"