The DHCP agent prioritizes RPC messages based on the
priority field send from neutron-server, but then groups
them all in the same dhcp_ready_ports set when sending
them back to the server to clear the provisioning block(s).
Priority should be given to new and changed ports, since
those are most likely to be associated with new instances
which can fail to boot if they are not handled quickly when
the agent is very busy, for example, right after it was
restarted.
Conflicts:
neutron/tests/unit/agent/dhcp/test_agent.py
Change-Id: Ib5074abadd7189bb4bdd5e46c677f1bfb071221e
Closes-bug: #1864675
(cherry picked from commit 113dfac608)
e2f01c65d9