Add support for the multiprovider API to ML2

This implements support for creating provider networks with
multiple different segments with the ML2 plugin.

Implements: blueprint ml2-multi-segment-api

Change-Id: Id6fc22841fddabfbe685de9605d4a4682ee1102d
ML2 Mechanism Driver for Cisco Nexus

Port of the quantum/plugin/cisco/nexus plugin to run under the Modular
Layer 2 (ML2) infrastructure as defined in
https://blueprints.launchpad.net/quantum/+spec/ml2-mechanism-drivers

Implements blueprint ml2-md-cisco-nexus

Change-Id: Ifdd03bec554a08266de859387f1901858a3be4a1
ensure that Arista test destroys the database

Out of order test execution has revealed that the database was not
properly cleaned up after each test run.  This patch adds a call to
clear the database after each test.

Fixes bug: 1220784

Change-Id: I8a706887f89f21ede88177e441a3b562fd8f74dc
Merge "Add support for the multiprovider API to ML2"
Merge "ML2 Mechanism Driver for Cisco Nexus"
Add l2 population base classes

This patch initiates the blueprint l2-population
Implemented as a ml2 Mechanism driver.

OVS & LinuxBridge drivers will be added as dependencies.

Rebased on ML2 Portbinding.

Change-Id: Ia2345aa262ec791c9f38b6e41e1e4b46f69cadac

Conflicts:

	setup.cfg
Vxlan / L2population support to Linuxbridge Agent

Vxlan support based on https://review.openstack.org/26516

This is a part of the blueprint l2-population

Change-Id: I99a961c53f9e451409f1affb079042936d8ae5c6

Conflicts:

	etc/neutron/plugins/linuxbridge/linuxbridge_conf.ini
	neutron/plugins/linuxbridge/agent/linuxbridge_neutron_agent.py