PodDisruptionBudget (PDB)可能会导致 Machine Config Operator 在 OpenShift 4 中降级

Issue

• 因为 machine-config-operator 降级，OpenShift 4 升级失败。

• MCP 被降级，并带有以下信息：

  pool is degraded because nodes fail with "1 nodes are reporting degraded
    status on sync": "Node [node_name]
    is reporting: \"failed to drain node: [node_name]
    after 1 hour. Please see machine-config-controller logs for more information\
  

• 在 machine-config-controller pod 的日志中出现消息错误：

  error when evicting pods/"[pod_name]" -n "[namespace_name]" (will retry after 5s): Cannot evict pod as it would violate the pod's disruption budget.