This fixes removals of the pid files and clean exit in the init script

Reviewed-by: iustinp

There is no point in initializing sigchld_handler as an empty dict, when
it will be overwritten by an instance of utils.SignalHandler
immediately after.

Reviewed-by: iustinp

This mainloop can be used in daemons like ganeti-noded.

Reviewed-by: iustinp