#13 spurius waitpid error after receiving EINTR

[Danny Faught]

I got this error after suspending stress_driver and
putting it in the background:

[02/13/105 12:19:16] (ERROR) exit_event: waitpid error
(returned 0): Interrupted system call

The waitpid needs to be restarted if it gets an EINTR
error. This should not be counted as an error condition.