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

Change-Id: I3f35ca4b81cc04987e20b5f136958fa3d80004ca
Reviewed-on: http://review.couchbase.org/37282
Reviewed-by: Philip Labee <philip@couchbase.com>
Tested-by: Philip Labee <philip@couchbase.com>