Fix traceback with '--iso <UNMOUNTABLE>' (#1044083)

There's no 'message' function in fedup.commandline.

So: make device_setup return the mountpoint of the device - unless the
mount fails, in which case it returns None. In that case we can print
the message and exit cleanly from the main script, like most other
errors.

Bonus: remove a gratuitous umount attempt (it happens automatically
thanks to atexit)

fedup.py

@@ -100,9 +100,12 @@ def main(args):
         return
 
     if args.device or args.iso:
-        device_setup(args)
+        mnt = device_setup(args)
 
         if args.iso:
+            if not mnt:
+                message('--iso: '+_('Unable to open %s') % args.iso)
+                raise SystemExit(2)
             log.debug("iso is %s", os.path.realpath(args.iso))
             def isocleanup():
                 log.debug("unmounting %s", args.device.mnt)
@@ -140,7 +143,6 @@ def isocleanup():
             print _("The '%s' repo was rejected by yum as invalid.") % args.instrepo
             if args.iso:
                 print _("The given ISO probably isn't an install DVD image.")
-                media.umount(args.device.mnt)
             elif args.device:
                 print _("The media doesn't contain a valid install DVD image.")
         else:

fedup/commandline.py

@@ -235,9 +235,9 @@ def device_setup(args):
             args.device = media.loopmount(args.iso)
         except media.CalledProcessError as e:
             log.info("mount failure: %s", e.output)
-            message('--iso: '+_('Unable to open %s') % args.iso)
-            raise SystemExit(2)
+            return
         else:
             args.repos.append(('add', 'upgradeiso=file://%s' % args.device.mnt))
             if not args.instrepo:
                 args.instrepo = 'upgradeiso'
+    return args.device.mnt