QtIFW

Fix and update how the sha files and packages are downloaded.

Fixes a possible messed up download chain once the archive download
failed. We need in turn call fetchNextArchiveHash as we will remove
both the hash and the package, though this does not reset the last
checksum and therefore the next proper archive download will compare
to the wrong SHA.

Change-Id: Ib4e569de4f5482123da7357a09b7bd087b5d6cbb
Reviewed-by: Niels Weber <niels.weber@digia.com>
Reviewed-by: Kai Koehne <kai.koehne@digia.com>