cbtransfer to tolerate all couchstore files

Recently there was an issue whereby a customer failed-over more nodes than they had replicas available and rebalanced. At this point, the only copy of the data they had were some copies of the couchbase data directories they had taken part-way through this bungled maintenance.

Some of the couchstore files on disk were active and these could be recovered without issue. However for some of the data, the only copy existed in replica or "none" (dead?) Couchstore files. Restoring from these was particularly problematic as the "--source-vbucket-state" parameter is only honoured when transferring from a cluster.

I appreciate that there is good reason for not wanting to pick up other couchstore files by default but in such true disaster recovery scenarios we need the tool to be less fussy about the data it is willing to restore. There are a few ways this might be accomplished - one might be to permit the --source-vbucket-state parameter to work on files also and accept "any" as a parameter, not just replica and active.