Remove -u option

Start memcached as the user you want it to run as

Change-Id: Iaf4c8f29ac36f2374108449b7144d1540b7519c5
Reviewed-on: http://review.couchbase.org/33078
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>