testnode: spawn with close_fds=True in ProcessManager

As leaving close_fds=False can result in subtle bugs (see
http://zderadicka.eu/subtle-evil-of-close_fds-parameter-in-subprocess-popen/ )
close descriptors before launching anything with ProcessManager, especially
useful for starting things like supervisord.

/reviewed-on nexedi/erp5!841

erp5/util/testnode/ProcessManager.py

@@ -166,7 +166,8 @@ class ProcessManager(object):
     logger.info('$ %s', command)
     sys.stdout.flush()
     p = subprocess.Popen(args, stdin=self.stdin, stdout=subprocess.PIPE,
-                         stderr=subprocess.PIPE, env=env, **subprocess_kw)
+                         stderr=subprocess.PIPE, env=env, close_fds=True,
+                         **subprocess_kw)
     self.process_pid_set.add(p.pid)
     timer = threading.Timer(self.max_timeout, timeoutExpired, args=(p,))
     self.timer_set.add(timer)