qemu: improve the error when try to undefine transient network
qemu: improve the error when try to undefine transient network

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1315059

Signed-off-by: Shanzhi Yu <98ab354c31cd9189e8ce8ab338c511d403e2f789@redhat.com>

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