Description of problem:
The metrics cassandra 3.9 has no permission to create directory /cassandra_data/data once Openshift is updated to v3.10. Redeploy metrics via  openshift-ansible:v3.10 can solve this issue. But there are some downtime between Openshift upgrade and metrics updated. 

To avoild the metrics downtime, we can add the securityContext to make v3.9 cassandra works in v3.10 as the following steps. if the customer don't care about the downtime, they can skip these steps.

Steps:
1. oc get namespaces openshift-infra -o json

$oc get namespaces openshift-infra -o yaml
apiVersion: v1
kind: Namespace
metadata:
  annotations:
    openshift.io/node-selector: ""
    openshift.io/sa.initialized-roles: "true"
    openshift.io/sa.scc.mcs: s0:c6,c5
    openshift.io/sa.scc.supplemental-groups: 1000040000/10000
    openshift.io/sa.scc.uid-range: 1000040000/10000
  name: openshift-infra
  uid: 2d73f159-8331-11e8-9c8f-42010af00028
spec:
  finalizers:
  - kubernetes
  - openshift.io/origin

2. Update the securityContext in replicacontrollers  hawkular-cassandra-1 using the values from the namespaces openshift-infra

  $oc edit rc hawkular-cassandra-1
   #Add the fsGroup and seLinuxOptions using the same value from the namespaces openshift-infra

                "securityContext": {
                    "fsGroup": 1000040000,
                    "seLinuxOptions": {
                        "level": "s0:c6,c5"
                    },
                    "supplementalGroups": [
                        65534
                    ]
                },
                "serviceAccount": "cassandra",
                "serviceAccountName": "cassandra"

For more detail, refer to https://bugzilla.redhat.com/show_bug.cgi?id=1590748, the PR https://github.com/openshift/openshift-ansible/pull/8831


Version-Release number of selected component (if applicable):
openshift-ansible:v3.9

How reproducible:
always

Steps to Reproduce:
1. deploy metrcis v3.9 on v3.9
  openshift_metrics_install_metrics=True
  oreg_url=registry.reg-aws.openshift.com:443/openshift3/ose-${component}:${version}

2. Upgrade OCP to v3.10

3. Check the cassandra logs in v3.10


Expected results:
The /cassandra_data/data can be access after upgrade

Additional info:
Once redeployed v3.10 via openshift-ansible:v3.10. The cassandra can acesss the directory /cassandra_data/data.