Update which signals are handled by cleanup.

[stephen-soltesz]

This change removes the unconditional loop that registers the 'cleanup' signal handler for all signals and registers the handler for specific signals that perform some action in cleanup.

This is to take advantage of the default implementations for SIGINT, SIGTERM, and SIGTSTP and to avoid unnecessary handling of all other signals.

[stephen-soltesz]

PTAL?

[pboothe]

LGTM