Merge pull request #55466 from x13n/addon-manager

Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.

Use results of kube-controller-manager leader election in addon manager

**What this PR does / why we need it**:
This adds leader election-like mechanism to addon manager. Currently, in a multi-master setup, upgrading one master will trigger a fight between addon managers on different masters, each forcing its own versions of addons. This leads to pod unavailability until all masters are upgraded to new version.

To avoid implementing leader election in bash, results of leader election in kube-controller-manager are used. Long term, addon manager probably should be rewritten in a real prgramming language (probably Go), and then, real leader election should be implemented there.

**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
I don't think there was an issue for this specifically, but this PR is related to https://github.com/kubernetes/kubernetes/issues/473

**Special notes for your reviewer**:

**Release note**:
```release-note
Addon manager supports HA masters.
```

cluster/common.sh

@@ -882,6 +882,11 @@ EOF
     if [[ "${NODE_ACCELERATORS:-}" == *"type=nvidia"* ]]; then
       cat >>$file <<EOF
 ENABLE_NVIDIA_GPU_DEVICE_PLUGIN: $(yaml-quote "true")
+EOF
+    fi
+    if [ -n "${ADDON_MANAGER_LEADER_ELECTION:-}" ]; then
+      cat >>$file <<EOF
+ADDON_MANAGER_LEADER_ELECTION: $(yaml-quote ${ADDON_MANAGER_LEADER_ELECTION})
 EOF
     fi