With the merging of #39996, salt/modules/docker.py now imports
salt.utils.docker. However, our loader appends the module dir (in
this case salt/modules/) to sys.path temporarily for the length of the
loading process. So, as the docker execution module tries to import
salt.utils.docker, when salt.utils.docker attempts to do an "import
docker", and docker-py is *not* installed, this results in
salt/modules/docker.py (the docker execution module) being loaded in its
place, which results in tracebacks in the minion log.
Renaming the docker execution module keeps this import shadowing from
occurring. Note that we don't need to do this for the placeholder
salt/states/docker.py as it does not import salt.utils.docker.
