Move memcached to cmake/

Change-Id: I96236d06091714894238e5a7d8cb58022e4ecbce
Reviewed-on: http://review.couchbase.org/29184
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>