thorium: messages must be grouped in workers to avoid clutter

[boisvert@bigmem biosal]$ lttng view | grep " message_number = 6014," trace |awk '{print $4" "$2}'
thorium_message:actor_send: (+0.000008638)
thorium_message:worker_send: (+0.000001009)
thorium_message:worker_enqueue_message: (+0.000000906)
thorium_message:worker_publish_message: (+0.000001557)

thorium_message:worker_pool_dequeue: (+0.005903591)
  ==> dequeue takes more time than the time required by a worker to process a message

thorium_message:node_send: (+0.000002957)
thorium_message:node_send_system: (+0.000002383)

thorium_message:node_dispatch_message: (+0.000130166)
  ==> this includes transportation between nodes

thorium_message:worker_pool_enqueue: (+0.000002907)
thorium_message:worker_enqueue_inbound_message: (+0.000001723)
thorium_message:worker_receive: (+0.000006593)
thorium_message:actor_receive: (+0.000027146)

Link: https://github.com/GeneAssembly/biosal/issues/751
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>
thorium: add thorium_worker tracepoints

Everything looks fine in the traces.

Link: https://github.com/GeneAssembly/biosal/issues/766
Signed-off-by: Sébastien Boisvert <boisvert@anl.gov>