Add test for non local mac address.

This test will pass after https://github.com/docker/libcontainer/pull/310 is merged.
Closes https://github.com/docker/docker/issues/9771.

Docker-DCO-1.1-Signed-off-by: Jessica Frazelle <jess@docker.com> (github: jfrazelle)
Shouldn't this actually test that the output contains the MAC specified?