util/testnode/ProcessManager: explicitly close file descriptors

this prevent ResourceWarnings on python3

erp5/util/testnode/ProcessManager.py

@@ -136,8 +136,6 @@ def killCommand(pid):
 
 class ProcessManager(object):
 
-  stdin = open(os.devnull)
-
   def __init__(self, max_timeout=MAX_TIMEOUT):
     self.process_pid_set = set()
     signal.signal(signal.SIGTERM, self.sigterm_handler)
@@ -176,7 +174,9 @@ class ProcessManager(object):
     logger.info('subprocess_kw : %r', subprocess_kw)
     logger.info('$ %s', command)
     sys.stdout.flush()
-    p = subprocess.Popen(args, stdin=self.stdin, stdout=subprocess.PIPE,
+
+    with open(os.devnull) as stdin:
+      p = subprocess.Popen(args, stdin=stdin, stdout=subprocess.PIPE,
                           stderr=subprocess.PIPE, env=env, close_fds=True,
                           **subprocess_kw)
       self.process_pid_set.add(p.pid)
@@ -189,6 +189,9 @@ class ProcessManager(object):
       result = dict(status_code=p.returncode, command=command,
                     stdout=stdout, stderr=stderr)
       self.process_pid_set.discard(p.pid)
+      p.stdout.close()
+      p.stderr.close()
+
       if self.under_cancellation:
         raise CancellationError("Test Result was cancelled")
       if raise_error_if_fail and p.returncode: