Honor TEST_RUNNER setting on runtests.py

[Leo Soto M.]

When running Django on Jython, we like to use a custom test runner to run the Django test suite. Unfortunately, runtests is hardcoded to use the simple runner bundled with Django.

It could be argued that I can always write my own runtests.py, but runtests itself is clearly not API-oriented and at least the whole django_tests function should be duplicated.

The attached patch is quite non-invasive and uses the runner specified on the settings, just as the "test" management command does.

[Eric Holscher]

Seems like a good idea. Marketing as accepted.

[Eric Holscher]

Triage fail.

[Malcolm Tredinnick]

(In [9918]) Fixed #10165 -- Use settings.TEST_RUNNER in runtests.py

This permits running Django's core tests under an alternative test runner. Most
likely useful to non-CPython implementations, rather than much else (since
Django's core tests might assume things about the test runner).

Patch from Leo Soto.