Api test - Users module

[Zizzamia]

Write test for all the api request in this page

Api
https://github.com/Opentaste/bombolone/blob/master/api/users.py

Core
https://github.com/Opentaste/bombolone/blob/master/core/users.py

Tests
https://github.com/Opentaste/bombolone/tree/master/tests/python