Make test_track_devices.cpp output easier to read.

Change-Id: I2d85cdbe591a6ee9763e742805f281cb26d7b122
diff --git a/adb/test_track_devices.cpp b/adb/test_track_devices.cpp
index 3e823e9..f78daeb 100644
--- a/adb/test_track_devices.cpp
+++ b/adb/test_track_devices.cpp
@@ -62,7 +62,7 @@
         if (!android::base::ReadFully(s, buffer, len))
             panic("could not read data");
 
-        printf( "received header %.*s (%d bytes):\n%.*s", 4, head, len, len, buffer );
+        printf( "received header %.*s (%d bytes):\n%.*s----\n", 4, head, len, len, buffer );
     }
     close(s);
 }