MDEV-5355: InnoDB assertion at shutdown if posix_fallocate is used in ut_a(node->n_pending == 0 || node->space->stop_new_ops); 

Analysis: When filespace is extended there is first prepare for IO. But if
posix_fallocate is used there was no complete IO causing assertion
at shutdown indicating that all IO is not finished.

Fix: If posix_fallocate is used to extend the filespace, there
is no need to wait for IO to complete, thus we treat this
operation as a read operation. We need to mark IO as
completed or there would be assertion on shutdown at
fil_node_close_file() because all pending IO is not finished.