common: fix early stop of panic

Add a join() to the thread, otherwise it happens that the main process
is already closed and the thread is still alive (because daemon = True).

This causes issues in tests, cause the returncode is 0 instead of -9, as
there was not enough time to execute the os.killpg before the main
thread ended.

Signed-off-by: Jean-Louis Dupond <jean-louis@dupond.be>

Author: dupondje

lib/vdsm/common/panic.py

@@ -23,3 +23,4 @@ def run():
         logging.shutdown()
     finally:
         ready.set()
+    t.join()