make python setup.py test return error codes (thanks sebdg)

In [1] we introduced catching errors raised during the installation of
Cuckoo. Due to the fact that we forgot to re-return the error code any
commands involving setup.py would always succeed. Including 'test' which
we use for unit testing with py.test.

[1]: 91c4985824

setup.py

@@ -139,6 +139,8 @@ def do_setup(**kwargs):
         if hasattr(e, "message") and isinstance(e.message, basestring):
             do_help(e, e.message)
 
+        exit(1)
+
 do_setup(
     name="Cuckoo",
     version="2.0.4.4",