Add `--quiet` to the `docker image pull` subcommand that will not pull
the image quietly.
```
$ docker pull -q golang
Using default tag: latest
```
Signed-off-by: Vincent Demeester <vincent@sbr.pm>
Also add TEST_DEBUG env variable for debugging E2E tests.
And change icmd environment helpers to fit the CmdOp interface os they
can be passed to 'icmd.RunCmd()'
Signed-off-by: Daniel Nephin <dnephin@docker.com>
Vincent Demeester
Daniel Nephin