qemu: driver: Move around code to avoid need to rollback
qemu: driver: Move around code to avoid need to rollback

qemuDomainChangeDiskLive rolled back few changes to the disk definition
if changing of the media failed. This can be avoided by moving some code
around.

fabianfreyer/libvirt,andreabolognani/libvirt,nertpinx/libvirt,datto/libvirt,nertpinx/libvirt,crobinso/libvirt,VenkatDatta/libvirt,andreabolognani/libvirt,taget/libvirt,jardasgit/libvirt,olafhering/libvirt,crobinso/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,olafhering/libvirt,datto/libvirt,eskultety/libvirt,andreabolognani/libvirt,taget/libvirt,datto/libvirt,jfehlig/libvirt,fabianfreyer/libvirt,nertpinx/libvirt,eskultety/libvirt,jfehlig/libvirt,jfehlig/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,zippy2/libvirt,fabianfreyer/libvirt,libvirt/libvirt,libvirt/libvirt,zippy2/libvirt,eskultety/libvirt,nertpinx/libvirt,taget/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,zippy2/libvirt,taget/libvirt,eskultety/libvirt,zippy2/libvirt,jfehlig/libvirt,crobinso/libvirt,libvirt/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,taget/libvirt,datto/libvirt,jardasgit/libvirt,crobinso/libvirt,olafhering/libvirt,nertpinx/libvirt,libvirt/libvirt,datto/libvirt,eskultety/libvirt,VenkatDatta/libvirt,jardasgit/libvirt,jardasgit/libvirt,olafhering/libvirt