Don't catch Throwable

### Affected version

head

### Bug description

We do this

```
        } catch (Throwable t) {
            onExit(-1, t.getClass().getSimpleName());
        }
```

in at least one place in GitPackCommand and in HgScmProvider. see https://stackoverflow.com/questions/6083248/is-it-a-bad-practice-to-catch-throwable for reasons not to do this