Support change of the patch-iso temp dir

This is useful when running pungi-patch-iso on VM with low amount of
memory but higher disk space. Without this option the operation will
fail because /tmp is tmpfs filesystem.

Signed-off-by: Jiri Konecny <jkonecny@redhat.com>

pungi/scripts/patch_iso.py

@@ -33,6 +33,9 @@ def main(args=None):
     parser.add_argument(
         "--force-arch", help="Treat the ISO as bootable on given architecture"
     )
+    parser.add_argument(
+        "--work-dir", help="Set custom working directory. Default: /tmp/", default=None
+    )
     parser.add_argument(
         "target", metavar="TARGET_ISO", help="which file to write the result to"
     )