cbtransfer doesn't like ephemeral buckets even when there's no attempt to copy the ephemeral bucket

To repro:

1. create 2 buckets: 1 couchbase "default", 1 ephemeral "eph"
2. populate some data in both
3. cp -R <data-directory> <tmp>
4. cbtransfer couchstore-files:///path/to/tmp couchbase://desthost:8091 -b default -B default -u Administrator -p password

You'll see the following even though you're not copying the eph bucket:

error: no vbucket_states in files: <data-directory>/eph/

Yes, the user can simply delete eph. However, there is a master.couch file in eph that instructs us that there are no docs to worry about so we don't have to error out when a cbtransfer is attempted.

$ couch_dbdump <data-director>/eph/master.couch.1 

Dumping "ns_server/data/n_0/data/eph/master.couch.1":

Total docs: 0