Un-indent after "pass" and "return" statements

Un-indent after "pass" and "return" statements
* lisp/progmodes/python.el (python-indent-block-enders): New var.
(python-indent-calculate-indentation): Use it.

* test/automated/python-tests.el
(python-indent-block-enders): New test.
(python-info-current-defun-2): Fix test.