Description of problem:

This is what's written in the docker-login man page:

... snip ...
Log in to a Docker Registry located on the specified SERVER.  You can
specify a URL or a hostname for the SERVER value. If you do not specify
a SERVER, the command uses Docker's public registry located at
https://registry-1.docker.io/ by default.  To get a username/password
for Docker's public registry, create an account on Docker Hub.
... snip ...

However, running 'sudo docker login' actually logs into https://registry.fedoraproject.org/v1/.

Version-Release number of selected component (if applicable):
docker-1.13.1-19.git27e468e.fc26.x86_64

How reproducible:
Always.

Steps to Reproduce:
[tadej@toronto ~]$ sudo docker login
Username: tjanez
Password: 
Login Succeeded

Actual results:
[tadej@toronto ~]$ sudo cat /root/.docker/config.json
{
	"auths": {
		"https://registry.fedoraproject.org/v1/": {
			"auth": "... removed ..."
		}
	}
}


Expected results:
Either 'sudo docker login' would login to Docker's public registry, i.e. https://index.docker.io/v1/, or the documentation is changed and users are instructed that they must use 'sudo docker login docker.io' to login to Docker's public registry.