PodDisruptionBudget (PDB) could cause Machine Config Operator to be degraded in OpenShift 4

Issue

• OpenShift 4 upgrade is failing due to machine-config-operator degraded.

• MCP is degraded with following message:

  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\
  

• Log message errors in machine-config-controller pod:

  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.