Agent/Job: Restore SIGINT to default_int_handler instead of SIG_DFL

SIG_DFL seems to exit the process, but we want the default python
handler that raises KeyboardInterrupt instead.

lnst/Agent/Job.py

@@ -96,7 +96,7 @@ def _run(self):
 
         os.setpgrp()
         signal.signal(signal.SIGHUP, signal.SIG_DFL)
-        signal.signal(signal.SIGINT, signal.SIG_DFL)
+        signal.signal(signal.SIGINT, signal.default_int_handler)
         signal.signal(signal.SIGTERM, signal.SIG_DFL)
 
         self._log_ctl.disable_logging()