MB-7435: Add more stats into tap-vbtakeover command

These stats provide more details on what the current state of the
tap stream is and will help in debugging.

Change-Id: Id15a8b13f930475ed3fc509709a3178e9b15ac20
Reviewed-on: http://review.couchbase.org/25886
Reviewed-by: Jin Lim <jin@couchbase.com>
Reviewed-by: Chiyoung Seo <chiyoung.seo@gmail.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>