Apply the label:
"node.kubernetes.io/exclude-from-external-load-balancers"
To control plane nodes to preserve backwards compatibility
with the legacy mode where "master" nodes were excluded from
LBs.
- Mark the "node-role.kubernetes.io/master" key for labels
and taints as deprecated.
- During "kubeadm init/join" apply the label
"node-role.kubernetes.io/control-plane" to new control-plane nodes,
next to the existing "node-role.kubernetes.io/master" label.
- During "kubeadm upgrade apply", find all Nodes with the "master"
label and also apply the "control-plane" label to them
(if they don't have it).
- During upgrade health-checks collect Nodes labeled both "master"
and "control-plane".
- Rename the constants.ControlPlane{Taint|Toleraton} to
constants.OldControlPlane{Taint|Toleraton} to manage the transition.
- Mark constants.OldControlPlane{{Taint|Toleraton} as deprecated.
- Use constants.OldControlPlane{{Taint|Toleraton} instead of
constants.ControlPlane{Taint|Toleraton} everywhere.
- Introduce constants.ControlPlane{Taint|Toleraton}.
- Add constants.ControlPlaneToleraton to the kube-dns / CoreDNS
Deployments to make them anticipate the introduction
of the "node-role.kubernetes.io/control-plane:NoSchedule"
taint (constants.ControlPlaneTaint) on kubeadm control-plane Nodes.
These are based on recommendation from
[staticcheck](http://staticcheck.io/).
- Remove unused struct fields
- Remove unused function
- Remove unused variables
- Remove unused constants.
- Miscellaneous cleanups
