Add create-nodes option for baremetal interface

Add a final, optional argument to create-nodes to define a specific
baremetal interface to be used and included as part of the name in
libvirt. This will allow us to define multiple TripleO test
environments on different bridges all on one machine/instance of
libvirt.

So we would run:

create-nodes $NODE_CPU $NODE_MEM $NODE_DISK $NODE_ARCH 1 brbm1

And result would be:

baremetalbrbm1_0 and baremetalbrbm1-0.qcow2

Behavior without this argument remains the same.

Also update cleanup-env to include cleanup of alternate seed and
baremetal named VMs.

Change-Id: I111d51ef3a817655284a28faca2ccd211d2241cc
Merge "Add create-nodes option for baremetal interface"