Vagrant: Make Debian and Centos builds functional

* Refactor bash and ruby code in vagrant setup
* Give unique names to VMs with Gporca and without
* add an example `vagrant-local.yml` that syncs `~/gpdb` with `rsync`
* Remove gp-xerces, use out-of-the-box Xerces instead
* use Bentobox builds for Debian and Centos
* Apply host's GPDB git configuration in VM: includes git user.name, user.email, clones from the same origin as user, adds all the user's remotes, and attempts to check out user's current remote/branch
* gitignore the .vagrant directories