VMware: add in DVS VXLAN support

The neutron network will be a VLAN port group or a VXLAN port group.
In the case of the latter the backend adds a VXLAX prefix to the
port group name.

The prefix is  'vxw-<dvs moref>-<virtual wiremoref>-sid-'

The patch supports both types of networks and enables VM's to have
network connectivity.

Change-Id: Icb93585eb486d4b6c8f141fd133971e2b0968f92
Merge "VMware: add in DVS VXLAN support"