tests: Fix random failures on el6

The reject tests were relaying on the behavior in Fedora 20, but on el6
the concurrent reject tests sometimes behaves differently. On Fedora 20,
recv() was always returning an empty string, but on el6, sometimes
socket.error "connection reset by peer" was raised.  Now both results
are considered as disconnection.

Change-Id: I7f6ad16bc2659318be3bb8dde4df5fee07af3417
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/34573
Reviewed-by: Piotr Kliczewski <piotr.kliczewski@gmail.com>
Reviewed-by: Dan Kenigsberg <danken@redhat.com>