CBQE-0: download build from latestbuilds if no release build

Change-Id: Ibaadb8d2eb1a6e1cc6f7488cf4adfe4ddf772080
Reviewed-on: http://review.couchbase.org/28011
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>