Add SAML metadata refresh control flag

mattdrayer: Change model fieldname, revise code, fix bad tests.

common/djangoapps/third_party_auth/migrations/0006_samlproviderconfig_automatic_refresh_enabled.py

@@ -0,0 +1,19 @@
+# -*- coding: utf-8 -*-
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('third_party_auth', '0005_add_site_field'),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name='samlproviderconfig',
+            name='automatic_refresh_enabled',
+            field=models.BooleanField(default=True, help_text=b"When checked, the SAML provider's metadata will be included in the automatic refresh job, if configured.", verbose_name=b'Enable automatic metadata refresh'),
+        ),
+    ]