qemu: checkpoint: Write metadata of previously-'current' checkpoint on update
qemu: checkpoint: Write metadata of previously-'current' checkpoint on update

Similarly to previous commit dealing with snapshots we must rewrite the
metadata of the previously-'current' checkpoint when changing which
checkpoint is considered 'current'.

Signed-off-by: Peter Krempa <2cf5c04c61aa466e4a47bfedc747d17279c72ffc@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

nertpinx/libvirt,zippy2/libvirt,zippy2/libvirt,jfehlig/libvirt,olafhering/libvirt,crobinso/libvirt,jfehlig/libvirt,jfehlig/libvirt,libvirt/libvirt,nertpinx/libvirt,crobinso/libvirt,crobinso/libvirt,olafhering/libvirt,libvirt/libvirt,zippy2/libvirt,zippy2/libvirt,libvirt/libvirt,nertpinx/libvirt,crobinso/libvirt,libvirt/libvirt,nertpinx/libvirt,olafhering/libvirt,jfehlig/libvirt,olafhering/libvirt,nertpinx/libvirt