Don't collect ns_server stats for non-kv nodes
Don't collect ns_server stats for non-kv nodes

Non-kv nodes don't collect stats so we should ignore them from our
collections.

Change-Id: I11e7ff85eea4b7fd7752e2a061c8ecbd276afedf
Reviewed-on: http://review.couchbase.org/49823
Reviewed-by: thomas anderson <faa2c0189873991686fbb8a0db4c162f340af90c@yahoo.com>
Tested-by: thomas anderson <faa2c0189873991686fbb8a0db4c162f340af90c@yahoo.com>

mikewied/cbagent,couchbase/cbagent,vmx/cbagent