Bug 1328173 - Switch test_no_missing_migrations to using check_changes
Bug 1328173 - Switch test_no_missing_migrations to using check_changes

Django 1.10 added a new check changes mode to the `makemigrations`
command, which we can use to avoid the hack of checking that the exit
code is 1 in the passing case:
https://docs.djangoproject.com/en/1.10/ref/django-admin/#cmdoption-makemigrations-check

KWierso/treeherder,tojonmz/treeherder,kapy2010/treeherder,KWierso/treeherder,edmorley/treeherder,tojon/treeherder,tojon/treeherder,edmorley/treeherder,edmorley/treeherder,KWierso/treeherder,tojonmz/treeherder,kapy2010/treeherder,KWierso/treeherder,tojonmz/treeherder,tojonmz/treeherder,tojonmz/treeherder,tojon/treeherder,kapy2010/treeherder,kapy2010/treeherder,kapy2010/treeherder,edmorley/treeherder,tojonmz/treeherder,tojon/treeherder