Fix AttachCurrentThread to use the right thread group.

Change-Id: I9818845c005563d894a571edc4f9be9862312380
diff --git a/src/jdwp/jdwp_main.cc b/src/jdwp/jdwp_main.cc
index f31eb0b..8fa650a 100644
--- a/src/jdwp/jdwp_main.cc
+++ b/src/jdwp/jdwp_main.cc
@@ -269,7 +269,7 @@
 
 void JdwpState::Run() {
   Runtime* runtime = Runtime::Current();
-  runtime->AttachCurrentThread("JDWP", true);
+  runtime->AttachCurrentThread("JDWP", true, Thread::GetSystemThreadGroup());
 
   VLOG(jdwp) << "JDWP: thread running";