Include tracerConfig in created tracing test

When creating prestate tracer tests in diff mode, the diff mode flag has
to be included in the resulting test JSON. This change makes sure the
flag is included in the JSON when it is passed to makeTest.

eth/tracers/internal/tracetest/makeTest.js

@@ -49,5 +49,6 @@ var makeTest = function(tx, traceConfig) {
         context: context,
         input:  eth.getRawTransaction(tx),
         result: result,
+        tracerConfig: traceConfig.tracerConfig,
     }, null, 2));
 }