NCBC-673: MEMD_ENOENT errors after failover nodes

When the configuration changes on a memcached bucket, the configuration
thread will raise an event on the provider. If the config revision has
changed, the new configuration will be loaded and the bucket using it will
be notified.

Change-Id: I2ef6cb35b7340b7d5542dccaa23b6ba726ac0a69
Reviewed-on: http://review.couchbase.org/41975
Tested-by: Jeffry Morris <jeffrymorris@gmail.com>
Reviewed-by: Mark Nunberg <mnunberg@haskalah.org>