Clean up all modulestore testcases
Move modulestore config for tests to an importable location
Disable pylnt warning for lms imports in common tests
Refactor all testcases that loaded all xml courses
TE-610
TE-489
Small fixes to modulestore test refactoring
Merge pull request #6078 from edx/zoldak/modulestore-test-refactor

Clean up all modulestore testcases