Add ovsbridge option to configure-vm

Adds a --ovsbridge for seed VMs. This will cause the public
interface on the seed to be placed on a ovs bridge as an
alternative to the default libvirt network.

Change-Id: Ia19d25087f9b8b21d9ff9da3a41b7a6131b081d9
configure-vm: refactor template formatting

Collapse the three copies of the bare metal NIC template and use the
same dict declaration style used earlier in the script.

Change-Id: I0263d7a3c35cf3ee208012539dddd5176f5dbc7a
Merge "Add ovsbridge option to configure-vm"
Merge "configure-vm: refactor template formatting"