Fails to build due to image_transport_py not being availble

[Jack17432]

image_transport_py does not seem to be available on Iron, and so when following the tutorial and rosdep from iron it fails to download all dependencies.

ERROR: the following packages/stacks could not have their rosdep keys resolved
to system dependencies:
image_transport_tutorials_py: Cannot locate rosdep definition for [image_transport_py]

[LuAPi]

It looks like it's available in kilted, but not versions before that - https://github.com/ros-perception/image_common/tree/kilted/image_transport_py . Ideally someone will update the tutorials and instructions to use that package to reflect this.