Possibly incomplete snapshots when an app fails to back up

[grote]

Because of binder space issues with many apps, we need to back up apps in chunks (of currently 100 apps). When a backup of an app in one chunk fails, the system may fail this entire chunk's backup. However, currently, we continue to request backup for the other chunks and include them into the snapshot and then show a success notification to the user. Still, there may have been more apps in the failed chunk to backup which will be missing from the snapshot.

We should consider not requesting backup of more chunks of packages, if the backup has already failed for one chunk
So we either re-include those packages somehow (may fail again in a loop!) or we simply fail the entire backup which may cause more failures for users :(

[grote]

Note that we show the number of apps in the success notification, so a attentive user may at least notice that this time less apps than usual were backed up.