Logging audit for guestagent/mongodb

Adjust logging to conform to logging standards.
Cleaned up a few messages that were unclear and changed several
LOG.info messages to LOG.debug.

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

Change-Id: I3bd544b761b449d1181792ff498f9c171331df16
Partial-Bug: #1324206
Merge "Logging audit for guestagent/mongodb"