ensure correct machine type gets saved on snapshot

ensure correct machine type gets saved on snapshot

instead of overwriting the 'machine' config in the snapshot,
use its own 'runningmachine' config only for the snapshot

this way, we do not lose the machine type if it was
explicitely set during the snapshot, but deleted afterwards

we also have to adapt the tests for this

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>