Removed unused imports and a "print" statement.
Disabled logging during tests.
Fixed PEP8 issues on tests.test_managers.
Fixed test cases that were failing due to inexistent search_indexes.py
Fixed core.tests.test_loading, given that it was not correct.

- This was due to code being committed without passing tests.
Removed dependency of test_models on logging.
Optimized imports of test_loading.