Non major core refactoring

Some utilities were grouped in new file mixins.py. This was done with
purpose of code spreading minimazing. Because of that two files are not
neede any more so they were deleted (utils/utils.py and wsgi_utils.py).
Unit and functional tests were updated.

Change-Id: Ia0752eaf145ca38b17a4d3f30b9c0e72566a1288
Merge "Non major core refactoring"