rpc api of ns_couchdb node

contains almost everything (with the exception of compaction_api)
that ns_server node calls on ns_couchdb node

in this commit it still calls ns_server node, because underlining
services are not moved to ns_couchdb node yet

Change-Id: Ica9dfc5cc88561bf939786bfe1fc9085d2f83edd
Reviewed-on: http://review.couchbase.org/41939
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
facility for collecting stats on ns_couchdb node

Change-Id: I90d77dddb078aad37b927dda2444604d86570423
Reviewed-on: http://review.couchbase.org/42150
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>