Comment 3 for bug 1656047

It's not a configuration problem: the docker rally image downloading url is configured here [1]:
docker.io/rallyforge/rally

But like it was said in description the docker.service is not running at the master node.
After I manually have started the docker I was able to pull image like test does:

[root@nailgun ~]# docker pull docker.io/rallyforge/rally
Using default tag: latest
Trying to pull repository docker.io/rallyforge/rally ...
latest: Pulling from docker.io/rallyforge/rally
f2e9c02f3e2d: Pull complete
a3ed95caeb02: Pull complete
Digest: sha256:5179baf1017c53f89390873db89c63e138e40bbd76daf800a63998239fe39345
Status: Downloaded newer image for docker.io/rallyforge/rally:latest
[root@nailgun ~]#
[root@nailgun ~]# docker images
REPOSITORY TAG IMAGE ID CREATED SIZE
docker.io/rallyforge/rally latest 04d16d90b65f 43 hours ago 720.9 MB

The root cause of problem is docker service doesn't start automatically after master node restart.
If we perform `systemctl enable docker.service` this will enables autostart of docker.

[1] https://github.com/openstack/fuel-qa/blob/8c798b4f370ea1c1e6c9a6f6a6dd169f825f7e8f/fuelweb_test/settings.py#L702