storage: Allow probe of volume capacity for BLOCK type
storage: Allow probe of volume capacity for BLOCK type

If the voldef type is VIR_STORAGE_VOL_BLOCK, then as long as the
format is known, let's allow the probe to happen - gets a truer value
and the same probe/update would be allowed for the same volume defined
in a domain.

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