thread_join.run: Put success message on new line

This patch makes sure that a line break is printed before the test
finishes. This way, the "Test succeeded" message is printed on a new
line, which was not always the case (i.e., on Pistachio) otherwise.

os/run/thread_join.run

@@ -34,6 +34,6 @@ build_boot_image "core init timer test-thread_join"
 
 append qemu_args "-nographic -m 64"
 
-run_genode_until {child exited with exit value 0.*} 10
+run_genode_until {child exited with exit value 0.*\n} 10
 
 puts "Test succeeded"