MB-11830 unless recreating don't resetVBucket on delVBucket

This change avoids writing an empty json failover table which
can cause tools like cbtransfer to fail
Change-Id: I658a08222800a4dc35b2c0b469de6cfbbbb8e9a4
Reviewed-on: http://review.couchbase.org/40039
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>