Attempt to fix build bot by including Dart VM flags when invoking testee.

runtime/bin/vmservice/observatory/test/test_helper.dart

Index: runtime/bin/vmservice/observatory/test/test_helper.dart
===================================================================
--- runtime/bin/vmservice/observatory/test/test_helper.dart	(revision 39151)
+++ runtime/bin/vmservice/observatory/test/test_helper.dart	(working copy)
@@ -23,8 +23,11 @@
 
   Future<int> launch() {
     String dartExecutable = Platform.executable;
-    print('** Launching $args');
-    return Process.start(dartExecutable, args).then((p) {
+    var fullArgs = [];
+    fullArgs.addAll(Platform.executableArguments);
+    fullArgs.addAll(args);
+    print('** Launching $fullArgs');
+    return Process.start(dartExecutable, fullArgs).then((p) {
 
       Completer completer = new Completer();
       process = p;