fdstreamtest: Print more info on read failure
fdstreamtest: Print more info on read failure

It helps with debugging if we know what's the return value of
saferead().

Signed-off-by: Michal Privoznik <83d82aaba2eed257f4814b0c239c260c4caaadf0@redhat.com>
Reviewed-by: John Ferlan <87558058f6f829e5ec976c8ef960720af4ff9c7d@redhat.com>

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