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
etcdctl was checking if the user exists before applying mutable calls;
if etcdctl contacts a minority member, the member may not know the user
exists on the cluster yet, causing command failure when it should succeed.
If the user does not exist, it will be picked up once the command goes
through raft.
Fixes#6932
