cmdVolCreateAs: Rework to follow usual func pattern
cmdVolCreateAs: Rework to follow usual func pattern

The way we usually write functions is that we start the work and
if something goes bad we goto cleanup and roll back there. Or
just free resources that are no longer needed. Do the same here.

Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>

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