qemu: snapshot: Translate 'volume' disks before attempting offline snapshot manipulation

qemu: snapshot: Translate 'volume' disks before attempting offline snapshot manipulation

When the VM is inactive the 'virStorageSource' struct doesn't have the
necessary data pointing to the actual storage. This is a problem for
inactive snapshot operations on VMs which use disk type='volume'.

Add the translation steps for reversion and deletion of snapshots.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1977155
Resolves: https://gitlab.com/libvirt/libvirt/-/issues/202
Signed-off-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>