calamari_ctl.py: move get_user_model import to initialize function

Having 'from django.contrib.auth import get_user_model' at the top of
the file causes an exception with Django 1.6 on openSUSE, due to
DJANGO_SETTINGS_MODULE not being set yet.  Moving the import to the
initialize function fixes this (although it violates PEP-8).

Signed-off-by: Tim Serong <tserong@suse.com>