Fix nova/pci direct use of object modules

This replaces all uses of nova.objects.<module>.<object> with
nova.objects.<object> within nova/pci and nova/tests/pci.

Change-Id: I72e763fb5032a5dc2cf649e5e29213ea71578c8d
Partial-Blueprint: object-subclassing
Merge "Fix nova/pci direct use of object modules"