django-pyscss is not compatible with Django 3.0.
django_pyscss_fix is a temporary workaround for django.utils.six
used in django-pyscss. It also add six in requirements.txt
as we use six module for this workaround.
This is just to run horizon for testing with Django 3.0+.
six is re-added to requirements.txt as it is used in the workaround.
Note that other codes in the horizon repo should not depend on six.
Change-Id: If79289b7518dd8eaf292a90d6fb790beb154cb7c