Raise the correct exception from AnyMsg.serialize

[drigz]

Previously, this was causing TypeError: 'module' object is not callable, which was not noticed due to the bare except: in the test.

I wasn't able to run the tests, so I'm relying on CI to test that part of the change. I tried running them within a ros:lunar docker container with:

catkin_make --pkg ros_comm
catkin_make run_tests_test_rospy_rostest

but got lots of errors like:

  File "/catkin_ws/src/ros_comm/clients/rospy/src/rospy/client.py", line 68, in <module>
    from roscpp.srv import GetLoggers, GetLoggersResponse, SetLoggerLevel, SetLoggerLevelResponse
ImportError: No module named srv

[dirk-thomas]

Thank you for the patch.

In the future please see the buildfarm documentation on how to reproduce the same build locally: https://github.com/ros-infrastructure/ros_buildfarm/blob/master/doc/jobs/devel_jobs.rst#run-the-devel-job-locally