Critical Alert Rules do not have runbook url

This bug is being raised by Openshift Monitoring team as part of effort to detect invalid Alert Rules in OCP.

1.  Check details of MultipleDefaultStorageClasses Alert Rule
2.
3.

The Alert Rule MultipleDefaultStorageClasses has Critical Severity, but does not have runbook_url annotation.

All Critical Alert Rules must have runbbok_url annotation

Critical Alerts must have a runbook, please refer to style guide at https://github.com/openshift/enhancements/blob/master/enhancements/monitoring/alerting-consistency.md#style-guide 

The runbooks are located at github.com/openshift/runbooks

To resolve the bug, 
- Add runbooks for the relevant Alerts at github.com/openshift/runbooks
- Add the link to the runbook in the Alert annotation 'runbook_url'
- Remove the exception in the origin test, added in PR https://github.com/openshift/origin/pull/27933