Cluster upgrade.[sig-arch] Check if alerts are firing during or after upgrade success

• alert.go
• runs after upgrade test suite

[sig-instrumentation][Late] [apigroup:config.openshift.io] [Suite:openshift/conformance/parallel]

• prometheus.go
• runs after conformance test suite

These two tests appear to use code that was once similar but both have drifted significantly. Get these onto common code so we have just one place to maintain.