Define a hypervisor driver method for getting MAC addresses.

This lets hypervisors export the MAC addresses an instance needs to have (or
return the default of None if the hypervisor is not constrained by MAC
addresses).  being provisioned.

Change-Id: I319a8deb2d09fbf8cecb7071256cf931924ef0e9
Break out a helper function for working with bare metal nodes.

This makes it easier to get a bare metal internal node id when called
from the manager.

Change-Id: I1b39a7be5bd21d5b3060f11a74b9eaf79b107210
Merge "Define a hypervisor driver method for getting MAC addresses."
Merge "Break out a helper function for working with bare metal nodes."