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/flow_expire.py b/tests/flow_expire.py
index ab5b68a..9be5fdd 100644
--- a/tests/flow_expire.py
+++ b/tests/flow_expire.py
@@ -17,7 +17,7 @@
 import oftest.parse as parse
 import basic
 
-from testutils import *
+from oftest.testutils import *
 from time import sleep
 
 #@var port_map Local copy of the configuration map from OF port