Filters can't exceed 4k, and GET requests against the GCE API are also
limited, so these break down in different ways at different cluster
counts. Fix it by introducing an advisory node-instance-prefix
configuration in the GCE provider that can hint the
EnsureLoadBalancer/UpdateLoadBalancer code (and the firewall
creation/update code). If it's not there, or wrong (a hostname that's
registered violates it), just ignore it and grab the whole project.