With etcd-manager the DNS names should only be used by the
etcd-manager pod itself, so we don't need to share /etc/hosts with the
host.
By not sharing we avoid:
(1) the temptation to address etcd directly
(2) problems of concurrent updates to /etc/hosts being hard from within a container (because locking is difficult across bind mounts)
Introducing with kubernetes 1.17 to avoid changing behavior of existing versions.
Refactor to start to centralize the env-var configuration for system
components, also start to add test coverage so we can be sure we
haven't broken things!
Justin SB