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/port_stats.py b/tests/port_stats.py
index 0964774..96d3cc5 100644
--- a/tests/port_stats.py
+++ b/tests/port_stats.py
@@ -17,7 +17,7 @@
 import oftest.parse as parse
 import basic
 
-from testutils import *
+from oftest.testutils import *
 from time import sleep
 
 #@var fs_port_map Local copy of the configuration map from OF port