Enable control plane to maintain during reboot

[zoetrope]

What

Maintenance operation does not run while reboot operation is running.

• Endpoints are not updated if one control-plane is down.
• controller-manager and scheduler do not recover if they crash.

How

Run reboot operation on another go routine

• Modify rebootOp as follows
  • after rebooting, remove cke.cybozu.com/reboot annotation
  • wait until the node is schedulable
  • remove the rebooted node from the reboot queue
• Modify rebootUncordonOp as follows
  • only uncordon for the node which is unschedulable and no cke.cybozu.com/reboot` annotation
• Register records of the reboot operation and do the operation by using a goroutine in order to avoid record registration conflicts with other operations.
• Disable sabakan integration for the certain period during a reboot operation in order to avoid the frequent master node change

Checklist

• [ ] Finish implentation of the issue
• [ ] Test all functions
• [ ] Have enough logs to trace activities
• [ ] Notify developers of necessary actions