Copying the entire docker service file isn't necessary to add an environment variable, instead use a drop-in configuration file. The nice side-effect is that the user gets any vendor updates to the docker.service file. Signed-off-by: Brandon Philips <brandon.philips@coreos.com> Upstream-commit: 2d51d71561565987fc6a600234f2e2d15e0ecf31 Component: engine