Description of problem:
Router default pods on OpenShift 4 fail [CIS Kubernetes Benchmark](https://www.cisecurity.org/benchmark/kubernetes/) recommendation 5.4.1 which states the following: "Prefer using secrets as files over secrets as environment variables".
`router-default` pods leverage secrets stored in STATS_PASSWORD and STATS_USERNAME environment variables which causes the benchmark to fail. See: https://github.com/openshift/cluster-ingress-operator/blob/master/pkg/operator/controller/ingress/deployment.go#L325-L344
In order for the benchmark to pass changes to the ingress-operator and router application will need to be made so that the stats credentials are sourced directly from a secret volume.
Version-Release number of selected component (if applicable):
Steps to Reproduce: