Use BaremetalNodes in the rack's nodes formset table

The formset table for editing rack's nodes need to get the
BaremetalNodes, not Nodes, because it needs all the info about CPUs,
Memory, etc.

Change-Id: I0ebaf3cb6a8cf075ac5574a7debf16e0291cb83d
Merge "Use BaremetalNodes in the rack's nodes formset table"