This change makes the etcd package compatible with the existing Go
ecosystem for module versioning.
Used this tool to update package imports:
https://github.com/KSubedi/gomove
Previous implementation watches a single key so there's no way
to have separate hosts associate with separate keys for a single
grpc target. Instead, accept all keys on a prefix.
Also fixes first the Next() to read current name data from etcd instead
of waiting for the next event on a synced watcher.
