Cannot run invalid_models tests individually from runtests.py

[floguy]

There is a small bug in runtests.py which prevents the invalid_models test individually from runtests.py.

[Russell Keith-Magee]

The problem definitely exists, but the solution isn't as simple as described. test_models is detritus of some kind; it's an empty list, and is never changed. The patch provided changes the way other tests can be invoked. Here's the validation cases:

./runtests --settings=XXX
should run the full suite (seems to be correct with patch)

./runtests --settings=XXX test_client_regress
should run 15 tests (with patch, runs 19)

./runtests --settings=XXX test_client_regress.AssertContainsTests
should run 1 test (with patch, runs 19)

[floguy]

Fixed the real problem. The tests were getting added just fine, but "test_labels" was still getting passed in along with the other apps. When the test runner attempted to import the "invalid_models" app, then everything crashed and burned. Simply removing that entry from test_labels keeps all other functionality intact while fixing the problem at hand.

[Russell Keith-Magee]

In [7576]: Fixed #6168 -- Updated the Django system test runner to make it possible to run the invalid_models test (and any other invalid_ test) explicitly, rather than just as part of the full suite. Thanks for tracking down the problem, Eric Florenzano.