The tripleo cloud uses dhcp, so make sure we override the nameserver
to point to localhost in that case.
Change-Id: If498925fc524ece91e2662a1d78008c8dce9d320
On all machines, set up unbound as a caching recursive resolver.
On single-use slaves, set it up to forward cache misses to the
DNS servers obtained by the template host on boot.
Change-Id: I8505f5a277f20b1328900a9a515cd84db77b2b3b