MB-9852 Notify pending connection when a pending vb becomes active

This change fixes a bug in notifying pending connections
when a vbucket state is transitioned from pending to active.

Change-Id: I5dd77f0f0c8d543808be3613d3d0336b4db01006
Reviewed-on: http://review.couchbase.org/31703
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>