storage: report VIR_ERR_NO_STORAGE_VOL when the file doesn't exist
storage: report VIR_ERR_NO_STORAGE_VOL when the file doesn't exist

Report VIR_ERR_NO_STORAGE_VOL instead of a system error when lstat
fails because the file doesn't exist.

Fixes this problem in virt-install:

  https://bugzilla.redhat.com/show_bug.cgi?id=1108922

Signed-off-by: Giuseppe Scrivano <20002b7b24c75512093a71a58285826d5c504fca@redhat.com>

datto/libvirt,elmarco/libvirt,zippy2/libvirt,jfehlig/libvirt,libvirt/libvirt,shugaoye/libvirt,eskultety/libvirt,nertpinx/libvirt,shugaoye/libvirt,nertpinx/libvirt,jardasgit/libvirt,rlaager/libvirt,agx/libvirt,nertpinx/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,fabianfreyer/libvirt,VenkatDatta/libvirt,jardasgit/libvirt,libvirt/libvirt,taget/libvirt,olafhering/libvirt,fabianfreyer/libvirt,fabianfreyer/libvirt,elmarco/libvirt,VenkatDatta/libvirt,datto/libvirt,agx/libvirt,VenkatDatta/libvirt,datto/libvirt,eskultety/libvirt,taget/libvirt,nertpinx/libvirt,taget/libvirt,agx/libvirt,elmarco/libvirt,jardasgit/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,elmarco/libvirt,zippy2/libvirt,fabianfreyer/libvirt,elmarco/libvirt,zippy2/libvirt,andreabolognani/libvirt,jardasgit/libvirt,crobinso/libvirt,shugaoye/libvirt,datto/libvirt,crobinso/libvirt,olafhering/libvirt,agx/libvirt,libvirt/libvirt,olafhering/libvirt,eskultety/libvirt,taget/libvirt,crobinso/libvirt,rlaager/libvirt,jfehlig/libvirt,eskultety/libvirt,VenkatDatta/libvirt,zippy2/libvirt,jfehlig/libvirt,jfehlig/libvirt,agx/libvirt,taget/libvirt,shugaoye/libvirt,eskultety/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,rlaager/libvirt,crobinso/libvirt,jardasgit/libvirt,shugaoye/libvirt,rlaager/libvirt,libvirt/libvirt,datto/libvirt,olafhering/libvirt,rlaager/libvirt,nertpinx/libvirt