Read stdout to avoid transferring before remote backup is done

openwrt_backup/retrieve.py

@@ -9,7 +9,8 @@ def make_backup_on_remote(client: SSHClient, tmp_path: Path):
     cmdline = ["sysupgrade", "-b"]
     remote_dest = tmp_path / "backup_latest.openwrt_backup.tar.gz"
     cmdline.append(remote_dest)
-    exec_remote(client, cmdline)
+    stdout, stderr = exec_remote(client, cmdline)
+    stdout.read()
     return remote_dest