move base test classes to oftest.base_tests

This lets them be shared between separate directories of tests.
diff --git a/tests/load.py b/tests/load.py
index a44b555..a05a373 100644
--- a/tests/load.py
+++ b/tests/load.py
@@ -26,12 +26,12 @@
 import oftest.dataplane as dataplane
 import oftest.action as action
 import oftest.parse as parse
-import basic
+import oftest.base_tests as base_tests
 import time
 
 from oftest.testutils import *
 
-class LoadBarrier(basic.SimpleProtocol):
+class LoadBarrier(base_tests.SimpleProtocol):
     """
     Test barrier under load with loopback