Fix vagrant-test template fix

Semplification and fix of vagrant-test template. To run a VM
and automatically install devstack and execute tempest, execute:

    $ cp local.conf.template local.conf
    $ ./runtest.sh

The support for devstack and the installation of libvirt and qemu
from git repositories is present.

Signed-off-by: Michele Paolino <m.paolino@virtualopensystems.com>