Implement etcd data loss recovery strategy

The initial MVP for HA etcd (HOSTEDCP-252) is fault tolerant except in cases involving member data loss.

This story is a placeholder to capture requirements around etcd disaster recovery scenarios involving member data loss, as described in the design document: https://docs.google.com/document/d/1AGMte79hUxNgkuGGFaAH24W8yU6w-obBH0d2lefWXtE/edit#.