Add domain server configuration option

The domain.d contains the cvmfs server priority to use for each
connected cvmfs domain.  This needs to be configured appropriate for
cloud location.  Set the string appropriate for servers on the west
coast of NA, since that is the location of the majority of our clouds.

Changes:
   * modified:   cvmfs/manifests/client.pp
   * new file:   cvmfs/templates/cern.ch.local.erb
   * modified:   gce_node/manifests/init.pp