Move rtd_tests/tests/base.py -> rtd_tests/base.py.

First step in reorganizing the rtd_tests directory so that only
tests are in the rtd_tests/tests/ directory.
Move mock_api.py into new rtd_tests/mocks dir.
Move rtd_tests/tests/files/ -> rtd_tests/files/.
Merge pull request #692 from toffer/rtd-tests-housekeeping

rtd_tests housekeeping