Fix a misconfiguration in swarming.py.

The TestObject expects a hard_time_out or io_time_out, not time_out. This
parameter has been ignored up to now. It's harmless but not useful. It is now
visible in the server's logs since the server noew prints out unknown parameters
since ef024b615ec50539f85f4cd2409296ce229a752b.

R=csharp@chromium.org
BUG=

Review URL: https://codereview.appspot.com/78210043
diff --git a/swarming.py b/swarming.py
index 9f82915..c447752 100755
--- a/swarming.py
+++ b/swarming.py
@@ -100,11 +100,13 @@
     self._isolate_item = None
     self._tasks = []
 
-  def add_task(self, task_name, actions, time_out=600):
+  def add_task(self, task_name, actions, time_out=2*60*60):
     """Appends a new task as a TestObject to the swarming manifest file.
 
     Tasks cannot be added once the manifest was uploaded.
 
+    By default, command will be killed after 2 hours of execution.
+
     See TestObject in services/swarming/src/common/test_request_message.py for
     the valid format.
     """
@@ -114,7 +116,7 @@
           'action': actions,
           'decorate_output': self.verbose,
           'test_name': task_name,
-          'time_out': time_out,
+          'hard_time_out': time_out,
         })
 
   def to_json(self):