Restructure down node processing.
Restructure down node processing.

Stepping stone to server group auto-failover.

Change-Id: I5e73143e1b2914a16395e7fdc98a7b7cf21c1a05
Reviewed-on: http://review.couchbase.org/85655
Well-Formed: Build Bot <80754af91bfb6d1073585b046fe0a474ce868509@couchbase.com>
Reviewed-by: Artem Stemkovski <15a0730a27c69f62ab86f2b6c639fca202166c02@couchbase.com>
Tested-by: Poonam Dhavale <6855f09986fe28ed7e8cdd9d60db878d898703d5@couchbase.com>

membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server,membase/ns_server