Remove redundant type field from MsgError

Also prefixed the generic names ERROR, SUCCESS
with MSG to avoid collision

Change-Id: Id1d060b4a4eabbbea380d4a84256b46f18ab686a
Reviewed-on: http://review.couchbase.org/38962
Reviewed-by: John Liang <johliang00@gmail.com>
Reviewed-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>
Tested-by: Deepkaran Salooja <deepkaran.couchbase@gmail.com>