Always forward to 8.8.8.8 on test nodes

Our providers have unreliable DNS in different ways.  Instead of
special casing all of them, just always forward queries to 8.8.8.8
until we have our own neutron-local recursive resolvers.

Closes-Bug: 1286963
Change-Id: I5eca2e2db75b38f829ba458bb8c3789646f562c2
Merge "Always forward to 8.8.8.8 on test nodes"