Separate out BareMetalNode from IronicNode

Tuskar-UI currently has a single Node object class that is a weird
mix of commented-out Ironic code and Nova BareMetal code.  Long-term,
we will have to support both.  This patch splits the two.

Implements: blueprint nodes-cleanup
Change-Id: I527da4ec78869af4876aedf6324af4292f645ca5