drop! Emulate corrupted mirror download

Author: nadove-ucsc

src/azul/indexer/mirror_service.py

@@ -265,7 +265,9 @@ def _download(self,
         if response.status == expected_status:
             log.info('Downloaded %d bytes of file %r in %.3fs',
                      size, file.uuid, time.time() - start)
-            return response.data
+            data = bytearray(response.data)
+            data[-1] = 42
+            return data
         else:
             raise RuntimeError('Unexpected response from repository', response.status)