fix test imports

These modules were previously visible through the testutils import.
diff --git a/tests/pktact.py b/tests/pktact.py
index 7d30698..905780e 100644
--- a/tests/pktact.py
+++ b/tests/pktact.py
@@ -17,6 +17,7 @@
 import time
 import unittest
 import random
+import scapy.all as scapy
 
 from oftest import config
 import oftest.controller as controller