Don't pass -u to memcached anymore

Change-Id: I7c2b3f0b6635cc195fafdc7352408c31a51058b2
Reviewed-on: http://review.couchbase.org/33222
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>