separate settings file for unittest

[siruku6]

references

• https://stackoverflow.com/questions/913549/how-to-unit-test-with-different-settings-in-django
• https://stackoverflow.com/questions/913549/how-to-unit-test-with-different-settings-in-django/30846788#30846788
• https://stackoverflow.com/questions/913549/how-to-unit-test-with-different-settings-in-django/41349685#41349685