* ci: make waiting for nodes more robust
After initializing the cluster, a lot of things happen in parallel and
are potentially getting in each others' way: nodes are joining,
daemonsets are proliferating, the network is being set up. During this
period, it's not unusual that the Kubernetes API server is unavailable
for a short time, e.g. due to etcd loosing quorum or load balancing
changes.
This period of instability has the potential to affect all kubectl
commands negatively, leading to problems especially for tests, where
command failures often lead to test failures. On the other hand, we'd
expect everything to be quite stable after the initial dust settles.
Therefore, this commit changes how we wait after initializing a cluster.
Until we have a reasonable expectation of readiness, we ignore command
failures and wait for things to stabilize. The cluster is considered
stable once all configured nodes and all API servers report ready.
