test_communication tests take a long time and provide unclear feedback on error

Bug report

Required Info:

• Operating System:
  • All
• Installation type:
  • All
• Version or commit hash:
  • 68c495a58df2502c77ebc972aba87c73ac46adcc
• DDS implementation:
  • All
• Client library (if applicable):
  • All

Steps to reproduce issue

colcon test --packages-select test_communication

Expected behavior

If failures exist, each test case terminates in a short (<1s) time and reports a relevant failure message (something like "10 messages were sent but 0 were received").

Actual behavior

On failure, the test takes a long time (10s) and the message only reports "timed out waiting for ... to finish". This makes it sound like the receiving process deadlocked. Additionally, the assertion uses a confusing string representation of the launch action object, where the subscriber executable name and arguments would be more appropriate.

https://ci.ros2.org/user/rotu/my-views/view/Extra%20RMW/job/nightly_linux-aarch64_extra_rmw_release/670/testReport/test_communication/TestPublisherSubscriber/test_subscriber_terminates_in_a_finite_amount_of_time_Arrays_/

Traceback (most recent call last):
  File "/home/jenkins-agent/workspace/nightly_linux-aarch64_extra_rmw_release/ws/build/test_communication/test_publisher_subscriber__rclpy__rclcpp__rmw_fastrtps_dynamic_cpp__rmw_cyclonedds_cpp_Release.py", line 66, in test_subscriber_terminates_in_a_finite_amount_of_time
    proc_info.assertWaitForShutdown(process=subscriber_process, timeout=10)
  File "/home/jenkins-agent/workspace/nightly_linux-aarch64_extra_rmw_release/ws/install/launch_testing/lib/python3.6/site-packages/launch_testing/proc_info_handler.py", line 144, in assertWaitForShutdown
    assert success, "Timed out waiting for process '{}' to finish".format(process)
AssertionError: Timed out waiting for process '<launch.actions.execute_process.ExecuteProcess object at 0xffff7e693e80>' to finish