Fixed issue with python3 input tests

This fixes the existing issue with running the input tests in python3. However, now that the python3 input test run, the `test_authorize_request` test fails with the same input as given in the python2 tests. I'm wondering if it has to do with the different code getting executed for python3 in the `base64encode_string` or `make_sha512_mac` functions in `core.py`.