[iso] Fix check on failable ISO

When ISO is marked as failable and check fails, the compose would still
be aborted. This patch fixes that

Signed-off-by: Lubomír Sedlář <lsedlar@redhat.com>

pungi/phases/createiso.py

@@ -268,6 +268,7 @@ class CreateIsoThread(WorkerThread):
         img.bootable = cmd["bootable"]
         img.subvariant = variant.uid
         img.implant_md5 = iso.get_implanted_md5(cmd["iso_path"])
+        setattr(img, 'can_fail', compose.can_fail(variant, arch, 'iso'))
         setattr(img, 'deliverable', 'iso')
         try:
             img.volume_id = iso.get_volume_id(cmd["iso_path"])