Review and update pull request #188

Reviewed and updated Pull Request #188 in https://github.com/vladimir-v-diaz/tuf/commit/2f520dd1409b6d59c856ec670192d8381cb4f48f

- [x] Merge and resolve "custom" FILEINFO changes.

Resolved custom fileinfo changes, disabled console log messages in `test_developer_tool.py', and fixed remaining issues with #188 (minor) in https://github.com/vladimir-v-diaz/tuf/commit/1985c450c910713e5b091aa806598923b4a74df1