Doesn't work on ROS2

[130s]

One of downstream packages that depend on rgbd_launch, openni2_launch, is being ported to ROS2 ros-drivers/openni2_camera#124. While I'm not yet sure if the dependency will be kept, we might as well assume it will?

[mikeferguson]

As with openni2_launch - I don't think we can actually make this work correctly until:

• All of the stuff in Connect/Disconnect notification/callback support ros2/rmw#330 (comment) gets merged so we can do proper lazy subscribers (which also means Iron is the first release that can support this)
• All of the various components we depend on in image_proc/depth_proc are updated to support lazy subscribers