Horizon still uses django.utils.importlib which is removed from Django
1.9. We should use:
from importlib import import_module
instead of:
from django.utils.importlib import import_module
Change-Id: I422e14546468cb9c5627e746023948aab107a338
Closes-Bug: #1534522
Partially-Implements: blueprint drop-dj17
Co-Authored-By: Rob Cresswell <robert.cresswell@outlook.com>