Do not run dataplane only by default

DataPlaneOnly was causing problems in some deployments and it
does not do much other than exercise the infrastructure.  Do
not run it by default.
diff --git a/tests/basic.py b/tests/basic.py
index 5ea03c6..0d90273 100644
--- a/tests/basic.py
+++ b/tests/basic.py
@@ -215,6 +215,8 @@
         # self.dataplane.show()
         # Would like an assert that checks the data plane
 
+test_prio["DataPlaneOnly"] = -1
+
 class Echo(SimpleProtocol):
     """
     Test echo response with no data