testnode: python3 fixes

Now that .spawn is called in tests, we can see that
getSupportedParameterList needs to take into account that on python3 the
program output is captured as bytes.

erp5/tests/testERP5TestNode.py

@@ -617,7 +617,7 @@ shared = true
     parser.add_argument('--hello_world', help='Hello world!')
     def spawn(*args, **kw):
       if args[1] == '--help':
-        return {'stdout': parser.format_help()}
+        return {'stdout': parser.format_help().encode()}
       call_parameter_list.append(args)
 
     test_node = self.getTestNode()

erp5/util/testnode/ProcessManager.py

@@ -196,8 +196,9 @@ class ProcessManager(object):
     return result
 
   def getSupportedParameterList(self, program_path):
-    return re.findall(r'^  (--\w+)',
-      self.spawn(program_path, '--help')['stdout'], re.M)
+    # type: (str) -> Sequence[str]
+    return (parameter.decode('utf-8') for parameter in
+        re.findall(br'^  (--\w+)', self.spawn(program_path, '--help')['stdout'], re.M))
 
   def killall(self, path):
     """