MB-8484: Allow version override for release tagging

Change-Id: I81c4e90322b6098727c4f8bf328b8fc3e8fc8a04
Reviewed-on: http://review.couchbase.org/27051
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>