remove __init__.py to let the new DiscoverRunner find the project

Django 1.6 integrated DiscoverRunner but removed its config options. If
discover_root is not set, it finds out the project root by starting to step
to parent directories until a directory without an __init__ file is found.

circle/circle/settings/test.py

-from base import *  # noqa
+from .base import *  # noqa
 
-########## TEST SETTINGS
-TEST_RUNNER = 'discover_runner.DiscoverRunner'
-TEST_DISCOVER_TOP_LEVEL = SITE_ROOT
-TEST_DISCOVER_ROOT = SITE_ROOT
-TEST_DISCOVER_PATTERN = "test_*.py"
 ########## IN-MEMORY TEST DATABASE
 DATABASES = {
     "default": {