MB-7933: Allow vbucket delete on non-dead vbuckets

Change-Id: I8d15ff21e22374c84436cdf15bcb49073b88db2f
Reviewed-on: http://review.couchbase.org/25335
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>