deploy-stub: flush output streams before exit

Intended to address #946

pandatool/src/deploy-stub/deploy-stub.c

@@ -724,6 +724,9 @@ int main(int argc, char *argv[]) {
   PyImport_FrozenModules = blobinfo.pointers[0];
   retval = Py_FrozenMain(argc, argv);
 
+  fflush(stdout);
+  fflush(stderr);
+
   unmap_blob(blob);
   return retval;
 }