When a Kubernetes cluster is instantiated in IPv6-only mode
via 'kubeadm init ...', the liveness probes that are
configured by kubeadm for kube-dns currently use IP:port
strings of "::1:53" and "::1:10053". These IP:port strings should
instead include brackets around the ::1 IPv6 loopback address, e.g.
"[::1]:53" and "[::1]:10053".
This change adds the necessary brackets around the ::1 IPv6 loopback
address.
Without this change, the kube-dns sidecar container interprets the
bracket-less strings as IPv4 IP:port strings that have too many
colons, and the kube-dns pod is restarted about once every 2 minutes.
fixes#56543
/area ipv6
/sig network
