Keep static analyzers like pyflakes happy about globals

_BASE_ENVIRON and _THE_NETWORK are set programmatically in main(), so static
analyzers think that they may not always be declared. So declare them as
global variables at the beginning and we're good.

lib/chutney/TorNet.py

@@ -24,6 +24,9 @@ import time
 import chutney.Templating
 import chutney.Traffic
 
+_BASE_ENVIRON = None
+_THE_NETWORK = None
+
 
 def mkdir_p(d, mode=0777):
     """Create directory 'd' and all of its parents as needed.  Unlike