Deal with breaking tests for 3.1

- Django's PostgreSQL JSONField wraps values in a JsonAdapter, so deal
  with that when it happens.  This goes away in Django 3.1.
- Setting related *_id fields clears the actual relation field, so
  trying to fake objects for tests is a problem
- Instance.objects.me() was inappropriately creating stub objects
  every time while running tests, but some of our tests now create
  real db objects. Ditch that logic and use a proper fixture where needed.
- awxkit tox.ini was pinned at Python 3.8

awxkit/tox.ini

@@ -8,7 +8,7 @@ skip_missing_interpreters = true
 # skipsdist = true
 
 [testenv]
-basepython = python3.8
+basepython = python3.9
 passenv = TRAVIS TRAVIS_JOB_ID TRAVIS_BRANCH
 setenv =
     PYTHONPATH = {toxinidir}:{env:PYTHONPATH:}:.