CheckErr prints a user friendly error to STDERR and exits with a non-zero exit code.

CreateClientAndWaitForAPI takes a path to a kubeconfig file, makes a client of it and waits for the API to be healthy.

KubernetesReleaseVersion is helper function that can fetch available version information from release servers based on label names, like "stable" or "latest".

WaitForAPI waits for the API Server's /healthz endpoint to report "ok".

WaitForPodsWithLabel will lookup pods with the given label and wait until they are all reporting status as running.