MB-7296 changed log rotation parameters for memcached

so it will keep 20 10MB logs

Change-Id: Ib4d2a50bc5914d922b652a8f45d938c8c55b05ba
Reviewed-on: http://review.couchbase.org/28986
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>