Assign a priority class to pods

[aveshagarwal]

Priority classes docs:
https://docs.openshift.com/container-platform/3.11/admin_guide/scheduling/priority_preemption.html#admin-guide-priority-preemption-priority-class

Example: https://github.com/openshift/cluster-monitoring-operator/search?q=priority&unscoped_q=priority

Notes: The pre-configured system priority classes (system-node-critical and system-cluster-critical) can only be assigned to pods in kube-system or openshift-* namespaces. Most likely, core operators and their pods should be assigned system-cluster-critical. Please do not assign system-node-critical (the highest priority) unless you are really sure about it.