Neutron fixups from ML2 testing

1. Shutdown virbr0 if running. This interface is created by libvirt and
currently we only disable it from starting at boot, but do not shutdown
the running interface.
2. Move root_helper into the [AGENT] section of neutron/l3_agent.ini to
quelch a warning.
3. Patch Neutron Open vSwitch kernel module version detection so it
works on new mainline kernels.
Merge remote-tracking branch 'upstream/master' into neutron-fixups-from-vxlan-ml2-branch
Merge remote-tracking branch 'upstream/master' into neutron-fixups-from-vxlan-ml2-branch
Merge remote-tracking branch 'upstream/master' into neutron-fixups-from-vxlan-ml2-branch
Merge pull request #310 from blueboxgroup/neutron-fixups-from-vxlan-ml2-branch

Neutron fixups from ML2 testing