No feedback from external node launcher

[m2-farzan]

We can't know if external nodes (or the launcher itself) are ready or not. We currently use open-loop timeouts but we should fix it soon.

Examples:

crl/test/02_runtime/test_04_external_nodes.py

Lines 18 to 20 in 9c83944

	launch_description = generate_launch_description()
	robot.runtime.ros_interface.launch_external_nodes(launch_description)
	await asyncio.sleep(10)

crl/src/cake/ros/interface.py

Lines 61 to 62 in 9c83944

	# Stabilize
	sleep(0.5)