Added support to configure cloud using ovs+vlan

To configure neutron using openvswitch with VLAN support set environment
variables `networkingplugin` to `openvswitch` and `networkingmode` to
`vlan`.
why not have $networkingmode instead of vlan? and change the test above to [ -n "$networkingmode" ]
could also be used independent of openvswitch so maybe split it