sysinfo: Kill the whole process-tree on daemon stop

It's possible that some daemons spawn other processes. Theoretically
killing the main process should clean everything, but to be certain
let's kill the full process tree (still it's possible the process
creates double-forked daemons which won't be killed, though).
Signed-off-by: NLukáš Doktor <ldoktor@redhat.com>

avocado/core/sysinfo.py

@@ -232,7 +232,7 @@ class Daemon(Command):
         """
         retcode = self.pipe.poll()
         if retcode is None:
-            self.pipe.terminate()
+            process.kill_process_tree(self.pipe.pid)
             retcode = self.pipe.wait()
         else:
             log.error("Daemon process '%s' (pid %d) terminated abnormally (code %d)",