pyloxi: start using data files for test cases

For the moment I'm just replacing the test functions one by one instead of
iterating over all test data files. We should think about doing that but I'm
not sure how to make failures easy to debug.
diff --git a/test_data/of10/action_bsn_set_tunnel_dst.data b/test_data/of10/action_bsn_set_tunnel_dst.data
new file mode 100644
index 0000000..7e1f43d
--- /dev/null
+++ b/test_data/of10/action_bsn_set_tunnel_dst.data
@@ -0,0 +1,10 @@
+-- binary
+ff ff # type
+00 10 # len
+00 5c 16 c7 # experimenter
+00 00 00 02 # subtype
+12 34 56 78 # dst
+-- python
+ofp.action.bsn_set_tunnel_dst(dst=0x12345678)
+-- python pretty-printer
+bsn_set_tunnel_dst { dst = 0x12345678 }