Make cleanup a param of mn, not a separate script

Also switch from print to info statements, to enable a non-verbose
clean.  Instead of 'mnclean', now run 'mn -c'.

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', 'mnclean']]
+            ['mn']]
 
 modname = distname = 'mininet'