Update OVS driver to work with objects

Update OVS driver to work with objects

This patch updates the QoS OVS driver to work with policy NeutronObjects
that are passed by the agent extension manager, instead of lists of rule
dicts, as we originally expected.  It also adds validation that the
rules that are sent by the neutron-server are actually supported by the
backend.

Finally, port dict was not really enough to determine the name of the
port in ovsdb. 'name' field is not really present in all port dicts, and
does not reflect what is known to ovs anyway. So instead, we should
rely on vif_port object to determine the ovs port name. Since ovs agent
only added the vif_port value to details dict when binding was desired,
I made adding the vif_port object unconditional, and covered that fact
with unit tests.

With this patch in place, I was able to get policy rules applied to a
port in devstack installation. Functional tests will belong to a
follow-up.

Partially-Implements: blueprint quantum-qos-api
Change-Id: I8926adb0a30728e4f82e55d71ad7e76676a22086