Fix memcached compatibility mode

The config given in create_memcached_compat() was rewritten by the
Couchbase configuration

Change-Id: Ic9c71e2b57adfd02f6f4ab635e6081a76f55ef27
Reviewed-on: http://review.couchbase.org/27975
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>