live: revisit error log when failing to validate checksum

Add explicit check for .full.sum after downloading it.

Rewrite errors log, one of them is misleading when checksum validation
fails, it refers to missing .full.sum, but it could be a different
reason.

src/live/ogOperations.py

@@ -219,7 +219,7 @@ class OgLiveOperations:
         if (not os.path.exists(image_path)):
             raise OgError(f'could not find {image_path} in cache')
         if (not tip_check_csum(repo, name)):
-            raise OgError(f'checksum file {name}.img.full.sum is missing in repository {repo}')
+            raise OgError(f'Failed to validate checksum for {name}.img')
 
         self._restore_image(image_path, devpath)
 

src/utils/tiptorrent.py

@@ -67,11 +67,14 @@ def tip_check_csum(tip_addr, image_name):
     logging.info(f'Verifying checksum for {image_name}.img, please wait...')
     image_path = f'{OG_CACHE_IMAGE_PATH}{image_name}.img'
     if not os.path.exists(image_path):
-        raise OgError(f'Invalid image path {image_path} for tiptorrent image csum comparison')
+        raise OgError(f'File {image_path} does not exist')
 
     cache_csum = _compute_md5(image_path)
     remote_csum = tip_fetch_csum(tip_addr, image_name)
 
+    if not os.path.exists(f"{image_path}.full.sum"):
+        raise OgError(f'File {image_path}.full.sum does not exist in repository {tip_addr}')
+
     if cache_csum == remote_csum:
         ret = True
         logging.info(f'Checksum is OK for {image_name}.img')