Improve etcd managed by docker UX

[bogdando]

The conf file with env vars cannot be used for docker run --env-file as is, because it contains double quotes and etcd fails to parse them from env vars. In order to improve UX for etcd managed by docker:

• Synch config opts from official docs
• Add a yaml conf file as well, see etcd upstream example. This allows to use docker run ... etcd --conf-file=foo.yml.