Add hacking test to block cross-virt driver code usage

The baremetal driver has been accessing some libvirt driver
private classes and config variables. Any code that is intended
to be shared across virt drivers should be in a common package
instead. Add a hacking file to enforce this for imports and
config options so that no further problems like this are made
in the future.

NB, this skips verification of the baremetal driver until
bugs 1261826 and 1261827 are fixed, or the baremetal driver is
removed, whichever comes first.

Change-Id: Ifbfe597795795a847830f9bd937dc459cd37d118
Closes-Bug: #1261842
Merge "Add hacking test to block cross-virt driver code usage"