Add worker prefix to all stdout lines

Change-Id: If4da68184f8e7e8ed9ec668719bd0b700b3e5d30
diff --git a/tools/thread_utils.py b/tools/thread_utils.py
index e92d2c8..397ebda 100755
--- a/tools/thread_utils.py
+++ b/tools/thread_utils.py
@@ -119,4 +119,5 @@
     if worker_id is None:
         print(msg)
     else:
-        print('WORKER %s: %s' % (worker_id, msg))
+        for line in msg.splitlines():
+            print('WORKER %s: %s' % (worker_id, line))