Split command when sending to subprocess.call on Linux platforms.

On the Linux platform (tested on Ubuntu 14.04, but this probably affects other platforms as well) the subprocess.call routine expects the call and its arguments split in a list. Behavior when using the entire string is platform dependent (unlike when sending a list) and, in this case, causes an error when attempting to randomize the MAC. Behavior using a list is platform independent so should generally be preferred. This makes that change for the Linux platform.