busybox

run-parts: add --exit-on-error | -e support

The "big" run-parts supports a handy --exit-on-error to stop execution on
errors, so lets support it as well.

Upstream doesn't have a short option for it, but I've used '-e' for busybox.

Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>