Add nicer wrapper function to throw CouchbaseErrors from python

So we don't have to pass a dict explicitly

Change-Id: I83bb3dc7ebd82d487311030865d4586a370ed231
Reviewed-on: http://review.couchbase.org/26606
Reviewed-by: Mordechai Nunberg <mnunberg@haskalah.org>
Tested-by: Mordechai Nunberg <mnunberg@haskalah.org>