JCBC-333: Only query nodes with active vbuckets.

Change-Id: I0bdfa213e1f8577a0ec1efee9c5191cf30792c38
Reviewed-on: http://review.couchbase.org/28693
Tested-by: Michael Nitschinger <michael.nitschinger@couchbase.com>
Reviewed-by: Matt Ingenthron <matt@couchbase.com>