OFAgent: Process port_update notifications in the main agent loop

Port the following patch to OFAgent.
commit: 5e6e592132aa9a98936ce3bfdb66efc7832caafb
https://review.openstack.org/#/c/61964/

Partial-Bug: 1293265

Conflicts:
	neutron/plugins/ofagent/agent/ofa_neutron_agent.py

Change-Id: I53813d12c66dc746cd373fd91ff9bd9bdbf222db
(cherry picked from commit 34e3be16a196c3da32cd6fa6147f6e00636a9aaf)
OVS and OF Agents: Create updated_ports attribute before setup_rpc

setup_rpc spawns rpc-consuming thread that can access
self.updated_ports before it is created in the constructor

Change-Id: Icc447c3bb7099125aae30e2430a6ad98ba00f6f9
Closes-Bug: #1314472
(cherry picked from commit 717a0a0ab4436e2904360fe4e34226af7d0e412d)
Default to setting secure mode on the integration bridge

Set the fail-mode on the integration bridge to be secure. This means if the agent
is stopped or crashes, and OVS is also restarted, OVS will not program a default
NORMAL action. As soon as the agent is restarted, it will correctly program the
integration bridge.

Change-Id: Icf7e3e14ee747c8ce92c14c95a0a1bbf35986252
Closes-Bug: #1324703
(cherry picked from commit 0412c8a3c43e77c1bb04b0c3ba4b2781fc52e7f8)
Merge "OFAgent: Process port_update notifications in the main agent loop" into stable/icehouse
Merge "OVS and OF Agents: Create updated_ports attribute before setup_rpc" into stable/icehouse
Merge "Default to setting secure mode on the integration bridge" into stable/icehouse