Fix 'module' object is not callable
* rhn_register: fix Python 3 compatibility
* rhn_register: update requirements
* rhn_register: add unit tests
* Add missing method name
* use a dedicated line for XML related requirements
* rhn_register: drop support for Python 2.4
* rhn_register unit tests: fix Python 3 compatibility
* refactor in order to check order of the requests
