Add .docker/config.json and support for HTTP Headers

This PR does the following:
- migrated ~/.dockerfg to ~/.docker/config.json. The data is migrated
  but the old file remains in case its needed
- moves the auth json in that fie into an "auth" property so we can add new
  top-level properties w/o messing with the auth stuff
- adds support for an HttpHeaders property in ~/.docker/config.json
  which adds these http headers to all msgs from the cli

In a follow-on PR I'll move the config file process out from under
"registry" since it not specific to that any more. I didn't do it here
because I wanted the diff to be smaller so people can make sure I didn't
break/miss any auth code during my edits.

Signed-off-by: Doug Davis <dug@us.ibm.com>
Upstream-commit: 18c9b6c6455f116ae59cde8544413b3d7d294a5e
Component: engine

components/engine/api/client/pull.go

@@ -42,8 +42,6 @@ func (cli *DockerCli) CmdPull(args ...string) error {
 		return err
 	}
 
-	cli.LoadConfigFile()
-
 	_, _, err = cli.clientRequestAttemptLogin("POST", "/images/create?"+v.Encode(), nil, cli.out, repoInfo.Index, "pull")
 	return err
 }