Remove backwards compatability in setup-baremetal

TripleO CI now populates the nodes array in the JSON datafile, so the
backward compatability code in setup-baremetal can be removed.

As an added bonus, nodes that specify more than one MAC address will
have all of them registered with nova-bm.

Change-Id: I7b8e7b67694319e377df400b122f16bff9e15370
Merge "Remove backwards compatability in setup-baremetal"