nose is not actively maintained now and Django default test runner
seems to have enough features.
* Horizon test setting no longer depends on nose and related stuffs.
This commit cleans up nose related dependencies.
The change was made in horizon Rocky-3,
so horizon 14.0.0.0b3 is required at least.
* Integraion tests is marked via django.test.tag mechanism which is
introduced in Django 1.10.
* Rename filename of test files to names starting with 'test_'
so that the django test runner can find tests expectedly.
* run_tests.sh is no longer called from tox.ini, so it can be dropped.
Note that the similar run_tests.sh in horizon was dropped long ago.
Change-Id: I1e5471078cc95031e8819f01100319a9ee2a3a73
72a6a7a94b