lb-agent: fix get_interfaces_on_bridge returning None

Change get_interfaces_on_bridge() to return [] instead of None
if the bridge is not found, as callers are expecting an iterator.

Change-Id: I359a2a0cf932c049f6891d4ba3eb8b9b23ab360d
Related-Bug: 1284311
BigSwitch: Create router ports synchronously

Since router ports are created as part of a
long transaction with multiple REST calls, they
need to be created sychronously. This is to prevent
the async thread from deleting them from the backend
if it can't find them in cases where they haven't been
committed to the DB yet.

Closes-Bug: #1305331
Change-Id: I2ab3c862dc6b1760199654bbd0969ac5efdbe704
Remove mock.patch.stop from tests that inherit from BaseTestCase

The tests that inherit from BaseTestCase don't need to stop their
patches, since this is already done in the base class

Change-Id: Ibb1183e521686d6e948046997b32f4044d91d9e7
Closes-bug: #1305656
NSX plugin: fix get_gateway_devices

Fixes the error and adds relevant unit tests.
Also fixes get_gateway_devices signature for allowing
paging and sorting.

Closes-Bug: 1306301

Change-Id: Icb52a764e111365beaf4dc4fb4a5b8970a6cf887
Merge "BigSwitch: Create router ports synchronously"
Merge "Remove mock.patch.stop from tests that inherit from BaseTestCase"
Merge "lb-agent: fix get_interfaces_on_bridge returning None"
Merge "NSX plugin: fix get_gateway_devices"
Add cookie support to ovs_lib, ovs_neutron_agent

All of the flows on the integration bridge belonging to a vif's
OpenFlow port are removed on port_bound. Since the firewall is invoked
to setup port filters before connectivity is established (i.e. before
port_bound is called) this defeats an OVS-based firewall. To solve
this issue, a distinct cookie on flows that belong to the firewall
and a separate, distinct cookie on flows that belong to the agent
will be used. This will require OVS version 1.5.0+ to delete flows
based on a cookie.

DocImpact: Adds configuration parameter to ovs_neutron_plugin.ini

Change-Id: Ia9b3aa6a383c3465f595725442eca2db05f24a16
Partially-implements: blueprint ovs-firewall-driver