create an all-in-one build for JBT projects, using submodules

Git 1.8.2 includes an option to have submodules track a branch tip, rather than specific commit IDs.

 "git submodule" started learning a new mode to integrate with the
   tip of the remote branch (as opposed to integrating with the commit
   recorded in the superproject's gitlink).

Therefore, while the solution nivologd@gmail.com has for his https://github.com/dgolovin/jbosstools-releng project is a decent option, it requires updating to stay current with branch tips. It's therefore only really as useful as it stays current.

If we can get Git 1.8.2 or newer installed on the Jenkins slaves, we could do a submodule build against whatever branch we wanted - master, 4.2.0.Alpha1x, etc.