Add logging for authentication handlers

Add logging for authentication handlers to the PolicyBasedAuthenticationManager.

This would also close PR #617.
I am working with an installation using the QueryDatabaseAuthenticationHandler.  This and #617 are my attempt to create some logging for it.  What you've said matches up with my experience so far with the QueryDatabaseAuthenticationHandler, and is why I chose an "error" logging level.  I don't know about the other authentication handlers.