Refactor CouchbaseBucket.LoadConfig and make it a proper IConfigInfo member

Change-Id: I99c895cd57966e0e5892a5c750dd68f0bad6d954
Reviewed-on: http://review.couchbase.org/40187
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>