Docker pull on docker store fails

[sflxn]

Docker pull on images on docker store fails. For instance,

docker pull store/ibmcorp/db2wh_ce:v2.9.0-db2wh_client-linux

Internal bug 2152747.

[sflxn]

I found the cause of this issue. We changed the default registry URL from registry-1.docker.io to registry.hub.docker.com as part of the content trust work. I didn't work on that and have no knowledge of it, and the people who made the changes do not remember why we made the change. In any case registry-1 is actually hardcoded in docker's code so I think we can just change it back and see if our ci build complains during the content trust tests.

I've also fixed a bug in the fetcher pertaining to interpretation of unauthorized access. It was presenting an improper error message leading me down the wrong path during debugging. We should now return access denied, which the docker registry code also returns.