Acquire vbucket lock on rollback operation with retry

rollback which writes a header to the vbucket file needs
synchronization with the flusher.

Change-Id: I05b2474e3bdcc5160c1b4e194ec2c2a2625533e3
Reviewed-on: http://review.couchbase.org/40019
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>