Resolved some warnings in tests.

[vytisb]

Also, added -Wall to tox config so that all warnings would be reported.

Resolved warnings:

RemovedInDjango110Warning: You haven't defined a TEMPLATES setting. You must do so before upgrading to Django 1.10. Otherwise Django will be unable to load templates.
RemovedInDjango20Warning: Importing from django.core.urlresolvers is deprecated in favor of django.urls.
RemovedInDjango20Warning: Old-style middleware using settings.MIDDLEWARE_CLASSES is deprecated. Update your middleware and use settings.MIDDLEWARE instead.
DeprecationWarning: assertDictContainsSubset is deprecated
ResourceWarning: unclosed file <_io.TextIOWrapper name='/home/vytis/src/django-celery/tests/someapp/tasks.py' mode='U' encoding='utf-8'>

[auvipy]

looks good and thanks for the PR. would be great to have the changelog/release notes.

[vytisb]

Added a changelog entry.