Feat: Prompt user if committing a file failed

[ezrizhu]

If we fail to commit a file, we should prompt the user on whether we should commit the rest or abort here. We could also let the user shell into the overlayfs and then rerun summary.

[mgree]

When might this happen? For something like #18 we should be deleting the original file... but I can imagine a race where the host system and the try process both create a file with the same name. If overlayfs doesn't crash when that happens, we should show that conflict in the summary.