CBQE-1886: cbrecovery tests should failed if there is not enough servers

Change-Id: Ic4b13b1254fb595f0ed93aec5a91fce6efeaf039
Reviewed-on: http://review.couchbase.org/32732
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Andrei Baranouski <andrei.baranouski@gmail.com>