Also add check to see if another controller is running -
eventually we should really detect errors from starting the
controller!!

Any code in mn is not usable by other Python code.

Hence, move this code into util, so other scripts can use it.

Now customConstructor, because it general to both links and nodes.

Note: we should probably rename it "setup()" to avoid confusion.

Also trying to fix NOX cmdline opt, but broken at the moment.

Controllers are no longer namespace-able, and all calls need one fewer
arg.

Also use more sensible temporary variable name.