MB-11708: set memcached_version to the sha1

Change-Id: I11f81c7285152c8ed350cbbdac5c178c09c1beaf
Reviewed-on: http://review.couchbase.org/39656
Tested-by: Trond Norbye <trond.norbye@gmail.com>
Reviewed-by: Dave Rigby <daver@couchbase.com>