Create a dummy device on TE hosts

To avoid registering the same MAC address on 2 seperate DHCP servers,
we create a dummy device to be used on the overcloud test network. This
isn't persisted across reboots but TE Hosts don't survive reboots anyway
so the overall situation is getting better.

Change-Id: I34df201a4beced1bb53ef2c1a3e19888eb989ed2
Related-Bug: #1272803
Merge "Create a dummy device on TE hosts"