Support SR-IOV networking in the PCI modules

This patch takes care of changing the PCI modules in support of SR-IOV
networking:
  -- Updated pci_whitelist to use devspec that is introduced in this
     patch: https://review.openstack.org/#/c/99043/
  -- For stats pool, to keep the existing behavior, pool keys always
     include product_id and vendor_id. Meanwhile, to work with tags
     and support pci requests based on tags, pools are ordered based
     on the number of keys of the pool. This makes sure that legacy
     pci requests will be satisfied with the pools in the beginning,
     possiblly with devices that are not tagged.

Partially Implements: blueprint pci-passthrough-sriov
Change-Id: I9da7bd921f098c958d6fb711a4d03a76862e95c7
Merge "Support SR-IOV networking in the PCI modules"