MB-5904 remove passwords from ns_config state

passwords were present in the state of 3 servers:
-ns_config
-ns_config_isasl_sync
-ns_config_log

could have been potentially exposed in case of the crash
of one of these servers

Change-Id: Iee8fe9ab59ac62a7da23f37e97f1745fc02bf49c
Reviewed-on: http://review.couchbase.org/28378
Reviewed-by: Artem Stemkovski <artem@couchbase.com>
Tested-by: Artem Stemkovski <artem@couchbase.com>