Start mongodb with --auth option

[warrenvw]

Moved from StackStorm/st2enterprise-dockerfiles#62

It is not recommended to run mongodb without authentication, for any length of time.

Some useful references:

• https://www.mongodb.com/blog/post/running-mongodb-as-a-microservice-with-docker-and-kubernetes
• http://pauldone.blogspot.com/2017/06/deploying-mongodb-on-kubernetes-gke25.html
• https://www.serverlab.ca/tutorials/linux/database-servers/how-to-create-mongodb-replication-clusters/

Chart has auth section to configure: https://github.com/helm/charts/tree/master/stable/mongodb-replicaset#authentication so should be doable with Helm values.yaml.

[arm4b]

Implemented via #63