Register CredentialType(s) every time Django loads

* Register all discovered CredentialType(s) after Django finishes
  loading
* Protect parallel registrations using shared postgres advisory lock
* The down-side of this is that this will run when it does not need to,
  adding overhead to the init process.
* Only register discovered credential types in the database IF
  migrations have ran and are up-to-date.

awx/main/tests/functional/test_apps.py

@@ -0,0 +1,26 @@
+import pytest
+
+from django.apps import apps
+
+
+@pytest.fixture
+def mock_setup_tower_managed_defaults(mocker):
+    return mocker.patch('awx.main.models.credential.CredentialType.setup_tower_managed_defaults')
+
+
+@pytest.mark.django_db
+def test_load_credential_types_feature_migrations_ran(mocker, mock_setup_tower_managed_defaults):
+    mocker.patch('awx.main.apps.is_database_synchronized', return_value=True)
+
+    apps.get_app_config('main')._load_credential_types_feature()
+
+    mock_setup_tower_managed_defaults.assert_called_once()
+
+
+@pytest.mark.django_db
+def test_load_credential_types_feature_migrations_not_ran(mocker, mock_setup_tower_managed_defaults):
+    mocker.patch('awx.main.apps.is_database_synchronized', return_value=False)
+
+    apps.get_app_config('main')._load_credential_types_feature()
+
+    mock_setup_tower_managed_defaults.assert_not_called()