feat: handle more exit signal

[eatradish]

No description provided.

[MingcongBai]

This might be problematic - and I assume that this pull request was made from @xry111's suggestion to make oma handle SSH disconnections - dpkg operations may be interactive (and especially when invoked by the user via oma upgrade, etc.).

Making oma continue to work past disconnection/window closing will likely make the situation more difficult for the user: they would have to kill debconf or dpkg whenever an interactive prompt shows up, whereas before they simply gets killed... Not to mention oma would attempt to retry failed operations before the next proceeds.