Renamed mn_run.py -> mn, mn_clean.py -> mnclean; updated Makefle

It's possible that mn_clean is a bit easier to read; mnclean may be easier
to type, however.

Added variables to Makefile so that source files are listed in a single
location.

setup.py

@@ -5,7 +5,7 @@ from setuptools import setup, find_packages
 from os.path import join
 
 scripts = [join('bin', filename) for filename in
-            ['mn_run.py', 'mn_clean.py']]
+            ['mn', 'mnclean']]
 
 modname = distname = 'mininet'