Disable migrations by default in unittests

Rendering model states when running migrate in Django 1.8 consumes
on the order of 4x-6x more memory than <1.8.

References:
* https://code.djangoproject.com/ticket/24745
* https://code.djangoproject.com/ticket/24743

This is causing failures in Jenkins as the workers run out of memory
and either processes cannot fork or the Out Of Memory Killer
kills a process that is running tests.

Disabling migrations until we do either or both of these:
* Upgrade to Django 1.9 and turn them back on. See EV-92 "Discovery: Upgrade edx-platform to Django 1.9"
* Address TE-1310 "Unit tests should be able to run without migrations"

docs/en_us/internal/testing.rst

@@ -173,12 +173,6 @@ To run these tests without ``collectstatic``, which is faster, append the follow
 
     paver test_system -s lms --fasttest
 
-For even more speed, use the ``--disable-migrations`` option to run tests without applying migrations and instead create tables directly from apps' models.
-
-::
-
-    paver test_system -s lms --disable-migrations
-
 To run cms python tests without ``collectstatic`` use this command.
 
 ::

pavelib/utils/test/suites/python_suite.py

@@ -18,7 +18,7 @@ class PythonTestSuite(TestSuite):
     def __init__(self, *args, **kwargs):
         super(PythonTestSuite, self).__init__(*args, **kwargs)
         self.opts = kwargs
-        self.disable_migrations = kwargs.get('disable_migrations', False)
+        self.disable_migrations = kwargs.get('disable_migrations', True)
         self.fasttest = kwargs.get('fasttest', False)
         self.subsuites = kwargs.get('subsuites', self._default_subsuites)