live: rewrite log in case tiptorrent client fails

Specify that image file cannot be found in cache because tiptorrent has failed,
otherwise it is confusing.

src/live/ogOperations.py

@@ -174,7 +174,7 @@ class OgLiveOperations:
             raise
 
         if (not os.path.exists(image_path)):
-            raise OgError(f'Image file {image_path} does not exist')
+            raise OgError(f'could not find {image_path} in cache')
         if (not tip_check_csum(repo, name)):
             raise OgError(f'checksum file {name}.full.sum is missing in repository {repo}')