image_uploader (attempt #3): fix images upload with no labels

If an image has no label, we set labels to {}; so to build tag_label in
that case we need to catch the TypeError exception or
tag_from_label.format(**labels) will raise, since labels would be NoneType.

We could have remove the default {} for Labels; but it's better to keep
it for further use in the image uploader; when the parameter is required
for certain methods.

Closes-Bug: #1857012
Depends-On: https://review.opendev.org/#/c/706196/
Change-Id: I35d73e7eca6f3cc208eda5d4c78a7bdd6cd7b810
(cherry picked from commit 1b4f32a28a)

tripleo_common/image/image_uploader.py

@@ -772,7 +772,7 @@ class BaseImageUploader(object):
                 tag_label = tag_from_label.format(**labels)
             except ValueError as e:
                 raise ImageUploaderException(e)
-            except KeyError as e:
+            except (KeyError, TypeError) as e:
                 if fallback_tag:
                     tag_label = fallback_tag
                 else: