Fix commit to updates

We definitely need to extract diff creation from sendemail, as it was not obvious at all that diffs are created both in 8-snapshots/20200324/.diff:AppStream:x86_64 paths when called from mksnapshot and on a tmp folder when called from movelinks.

For now, since we only commit when updating prod links and so on, this MR will do the trick. I will propose the refactor in a different MR.