Recent builds of the metrics cassandra image for openshift 3.6 appear to require a truststore to be configured to allow secure communication between cassandra nodes.
When starting the openshift template with the latest openshift-metrics container image (brew-pulp-docker01.web.prod.ext.phx2.redhat.com:8888/openshift3/metrics-cassandra:3.6.0), the cassandra start script returns the following error:

The --truststore_node_authorities value is not specified. Aborting