Make the "clean" operation interruptible.

Change-Id: I60f221a0dfcc2786dfaa6b655cbce7f899a2027b
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Fix crash on product disabling.

Task-number: QBS-561
Change-Id: Ia56280cb26241c7fb9debd0d4ce1349b041405a6
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>