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
Fix VirtualInterfaceMacAddressException message

Previous the message reflected the default value of
create_unique_mac_address_attempts configuration option.

Changed to a generic message.

Change-Id: I55c5f95cfc7ac4183e08a7880cbbb9670a02cef4
Closes-Bug: #1276312
Stacktrace on error from libvirt during unfilter

We are seeing this issue freqently in the gate, but we don't have any
stacktrace for what is happening.  An error from libvirt is an
unexpected exception and should include a stacktrace.

Related-Bug: #1275256
Change-Id: If7c0e19aba7a3d129f4b82f52d86b8e3b6a0a194
Merge "Stacktrace on error from libvirt during unfilter"
Merge "Fix VirtualInterfaceMacAddressException message"
Add XenAPI driver deprecation warning log message

The XenAPI driver does not have running CI and per the schedule,
is slated for deprecation in Icehouse-3. This adds the warning
message to the log to alert admins to this fact, in line with the
others we have been adding for drivers in similiar situations.

Change-Id: Iaff48aaca27d87c600291b8abcc23273a879366a
Merge "Add hacking test to block cross-virt driver code usage"