Switch to stestr in README.rst and the method name

This commit switches to stestr in README.rst and the method name. We
already switched to use stestr instead of testr/ostestr. However,
a few are still remaining in README.rst and the unit test name. This
patch leaves some `testr` things because they are for the 'legacy run
method'. So, we don't need to remove them completely.

Change-Id: I0e8e19e2150d6e0ce9a299a10bdd51652d86497e
diff --git a/README.rst b/README.rst
index 2243536..e9de77e 100644
--- a/README.rst
+++ b/README.rst
@@ -109,15 +109,18 @@
 
     $ tempest run --workspace cloud-01
 
-   There is also the option to use testr directly, or any `testr`_ based test
-   runner, like `ostestr`_. For example, from the workspace dir run::
+   There is also the option to use `stestr`_ directly. For example, from
+   the workspace dir run::
 
-    $ ostestr --regex '(?!.*\[.*\bslow\b.*\])(^tempest\.(api|scenario))'
+    $ stestr run --black-regex '\[.*\bslow\b.*\]' '^tempest\.(api|scenario)'
 
-   will run the same set of tests as the default gate jobs.
+   will run the same set of tests as the default gate jobs. Or you can
+   use `unittest`_ compatible test runners such as `testr`_, `pytest`_ etc.
 
+.. _unittest: https://docs.python.org/3/library/unittest.html
 .. _testr: https://testrepository.readthedocs.org/en/latest/MANUAL.html
-.. _ostestr: https://docs.openstack.org/os-testr/latest/
+.. _stestr: https://stestr.readthedocs.org/en/latest/MANUAL.html
+.. _pytest: https://docs.pytest.org/en/latest/
 
 Library
 -------