[jsk_topic_tools] Add diagnostic transport to ConnectionBasedTransport

[iory]

What is this?

This PR has added the ability to output diagnostics to the ConnectionBasedTransport.

Checking the node status by diagnostics

You can check diagnostics by setting ~enable_vital_check to true.

# terminal 1:
$ roslaunch jsk_topic_tools sample_connection_based_transport.launch

# terminal 2:
$ rostopic list
/diagnostics
/diagnostics_agg
/diagnostics_toplevel_state
/input
/input_dummy
/input_image
/mux/selected
/rosout
/rosout_agg
/simple_image_transport/output

# terminal 3:
$ rosrun rqt_robot_monitor rqt_robot_monitor

There is no one to subscribe to /simple_image_transport/output, so diagnostics is OK.

# terminal 4:
rostopic echo /simple_image_transport/output

If you subscribe to /simple_image_transport/output,
it will change to the diagnostics message /simple_image_transport is running.

# terminal 5:
rosservice call /mux/select input_dummy

When changing input for simple_image_transport by mux, the error message will change to /simple_image_transport is not running.

You can check if the node is running correctly like these.

[k-okada]

If this feature is designed for human operator to observe the health of robot system on rqt_robot_monitor?, please add image of diagnostic viewer.

[iory]

OK. I'll add it.

[iory]

Added it.
https://github.com/jsk-ros-pkg/jsk_common/blob/ca3348bec3dd638f9cebc24bbcea3b79ef576dee/doc/jsk_topic_tools/class/python_connection_based_transport.md

[k-okada]

instead of create new class, how about update ConnectionBasedTransport and enable this feature when /use_vital_check_on_connection_based_transport(or other good variable name) is true

[iory]

That's a good idea!
I merge diagnostic function to ConnectionBasedTransport.
c8efdb1