utils: add error checks to checksum file creation in tip_write_csum

Add a check for potential permission or IO errors during the
creation of the image checksum.

src/utils/tiptorrent.py

@@ -51,8 +51,11 @@ def tip_write_csum(image_name):
 
     filename = image_path + ".full.sum"
     csum = _compute_md5(image_path)
-    with open(filename, 'w') as f:
-        f.write(csum)
+    try:
+        with open(filename, 'w') as f:
+            f.write(csum)
+    except OSError as e:
+        raise OgError(f'Could not write {filename}, reported: {e}') from e
 
     return csum