Add support for configuring OVS to work with OpenDaylight

This adds support for running OpenDaylight as an OpenStack Neutron plugin
under devstack. This entails downloading the latest version of OpenDaylight,
configuring it, and running it as a service under devstack. This code also
includes pieces which configure Open vSwitch on each devstack node to point
at OpenDaylight as their OpenFlow and OVSDB control interface. This is
required for compute hosts, which will not be running any Neutron software
on them at all. This post-devstack configuration is handled in the extras
directory because of the fact there is no Neutron code running on the compute
hosts themselves.

Closes-bug: #1273917

Change-Id: I696e7c7fe63c835f90c56105775def305a702877
Merge "Add support for configuring OVS to work with OpenDaylight"