Signal handling meta-issue

[pvdrz]

trafficstars

This issue tracks if sudo-rs behaves the same as ogsudo when receiving certain signals:

• [x] SIGALRM: Tracked by #448
• [x] SIGCHLD: This is indirectly tested by the fact that we handle SIGCHLD by waiting for child processes but we shouldn't misbehave if someone sends us a fake SIGCHLD.
• [ ] SIGCONT
• [ ] SIGHUP
• [ ] SIGINT
• [ ] SIGKILL: It is not possible to handle this signal but we shouldn't leave child processes hanging around.
• [ ] SIGQUIT
• [ ] SIGSTOP: It is not possible to handle this signal
• [x] SIGTSTP: Tracked by #325
• [ ] SIGTERM
• [ ] SIGTTIN
• [ ] SIGTTOU
• [ ] SIGUSR1
• [ ] SIGUSR2
• [ ] SIGWINCH

This should be tested with and without a pty for every process that sudo creates.