Remove default=None when set value in Config

By default oslo.cfg sets the default values as None [1], there is
no need to explicitly do this.

[1] https://github.com/openstack/oslo.config/blob/master/oslo_config/cfg.py#L829

Change-Id: I5cba77d5502077e2323f4e86e0d29364eabf9c4c

aodh/cmd/alarm_conversion.py

@@ -81,7 +81,6 @@ def get_parser():
     )
     parser.add_argument(
         '--alarm-id',
-        default=None,
         type=str,
         help='Only convert the alarm specified by this option.',
     )

aodh/event.py

@@ -34,7 +34,6 @@ OPTS = [
                help='Number of notification messages to wait before '
                'dispatching them.'),
     cfg.IntOpt('batch_timeout',
-               default=None,
                help='Number of seconds to wait before dispatching samples '
                'when batch_size is not reached (None means indefinitely).'),
 ]

aodh/notifier/__init__.py

@@ -35,7 +35,6 @@ OPTS = [
                help='Number of notification messages to wait before '
                     'dispatching them.'),
     cfg.IntOpt('batch_timeout',
-               default=None,
                help='Number of seconds to wait before dispatching samples '
                     'when batch_size is not reached (None means indefinitely).'
                ),