Report step number when a test case fails

Allow test code to declare a "step number". Report the current step
number when a test fails.
diff --git a/tests/suites/target_test.function b/tests/suites/target_test.function
index 91f7198..937e8dd 100644
--- a/tests/suites/target_test.function
+++ b/tests/suites/target_test.function
@@ -375,6 +375,7 @@
     {
         ret = 0;
         test_info.result = TEST_RESULT_SUCCESS;
+        test_info.step = (unsigned long)( -1 );
         data_len = 0;
 
         data = receive_data( &data_len );