Feature/sections sapna unittests

Fixed unit tests for create_section_form, get_enrollments_without_test_student , remove_section and created separate test files for these. Also added new test casesin these methods for the new utilities 'check_resource_link_id' and 'validate_course_id'
I think this is for the outter most exception in the view. If that's not correct, then I'm not sure what this is actually testing. If I am right, I think it should make sure that the error template was rendered with a status of 500.