Revert "MB-4345 Use unique admin memcached password on each node."

This reverts commit 098c3fed6966aec8c19b5059d534fb41535dbe4e.

Change-Id: Ifb8fe8c7caf38af31d8570e2a386b6066c221fbd
Reviewed-on: http://review.couchbase.org/28984
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>
Tested-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>