Group global imports at the top

lib/chutney/Traffic.py

@@ -20,6 +20,7 @@
 #
 # For example code, see main() below.
 
+import sys
 import socket
 import select
 import struct
@@ -325,8 +326,6 @@ class TrafficTester():
             s.close()
         return self.tests.all_done() and self.tests.failure_count() == 0
 
-import sys
-
 
 def main():
     """Test the TrafficTester by sending and receiving some data."""