Alertmanager and Prometheus crashes because 9094 port was already in use in OpenShift 3.11

Issue

• After a new deploy, alertmanager and prometheus pods are in crash state:

# oc get pods
NAME                                           READY     STATUS             RESTARTS   AGE       IP             
alertmanager-main-0                            2/3       CrashLoopBackOff   2465       8d        X.Y.Z.X    
alertmanager-main-1                            2/3       CrashLoopBackOff   2467       8d        X.X.X.X   
alertmanager-main-2                            2/3       CrashLoopBackOff   2467       8d        Y.Y.Y.Y   
cluster-monitoring-operator-7b4559f448-t8gng   1/1       Running            0          8d        Z.Z.Z.Z     
grafana-784cc56d8f-gzmjh                       2/2       Running            0          8d        X.Z.X.X   
prometheus-k8s-0                               3/4       CrashLoopBackOff   2523       8d        Y.X.Y.Y   
prometheus-k8s-1                               4/4       Running            2574       8d        Z.X.Z.Z    
prometheus-operator-6cbcd4bcf6-lm6hg           1/1       Running            0          8d        Z.Y.Z.Z