[ros] video_camera: possibility to disable tf publisher

To solve #521 
should be
```python
if self.kwargs.get('pub_tf', True):
    self.publish_with_robot_transform(image)
else:
    self.publish(image)
self.topic_camera_info.publish(camera_info)
```
CameraInfo only defines meta information for a camera.
* http://docs.ros.org/api/sensor_msgs/html/msg/CameraInfo.html 

And since `default` method is called periodically,
it might be better to create a member variable instead of calling `self.kwargs.get`.