CBLT-302:  pass in BUILD_NUMBER as parameter, not env.var.

Change-Id: Ic6838609ba75e7f11664cb27a94cc922caa9bbea
Reviewed-on: http://review.couchbase.org/37281
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>