Create mock environment to test cases in test_settings

[jonespm]

The test for test_settings.py tests values set on the settings which are read from the environment. We either should set some mock values against the settings or have them set in the environment with something like monkeypatch.setenv or probably more likely SimpleTestCase.settings() to actually test that these settings are loaded correctly with different sets of settings.

I'd also include a test case for REDIS_HOST that includes spaces.

Originally posted by @jonespm in #473 (review)