[dev_io] signal_actor actor does not exit cleanly and leaks on exit

[lerwys]

Problem: We are not saving the generated pipe when starting the signal_actor thread here: https://github.com/lnls-dig/halcs/blob/master/src/dev_io/dev_io_core.c#L1549

Thus, we leak when destroying dev_io. Even worse, we should refactor this thread to avid dealing with signals directly.