We discover the kops-controller in gossip mode using seeding code that
calls into the GCE API, just like gossip itself does.
We refactor the gossip code into a shared gcediscovery library with
minimal dependencies.
kops-controller can now serve the instance group & cluster config to
nodes, as part of the bootstrap process.
This enables nodes to boot without access to the state
store (i.e. without S3 / GCS / etc permissions)
Feature-flagged behind the KopsControllerStateStore feature-flag.