move testutils to src/python/oftest

testutils.py needs to be in a common location for different directories of
tests to use it.
diff --git a/tests/basic.py b/tests/basic.py
index 721f953..53947b4 100644
--- a/tests/basic.py
+++ b/tests/basic.py
@@ -31,7 +31,7 @@
 
 import oftest.illegal_message as illegal_message
 
-from testutils import *
+from oftest.testutils import *
 
 #@var basic_port_map Local copy of the configuration map from OF port
 # numbers to OS interfaces