zilencer: Remove uniqueness constraint on RemoteZulipServer.hostname.

Enforcing the unique constraint adds an unnecessary support burden for
figuring out who actually controls a given hostname, and in particular, for
verifying updates to the org id/key on a re-install of the Zulip server.

zilencer/migrations/0007_remotezulipserver_fix_uniqueness.py

@@ -0,0 +1,20 @@
+# -*- coding: utf-8 -*-
+# Generated by Django 1.11.11 on 2018-04-30 06:55
+from __future__ import unicode_literals
+
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('zilencer', '0006_customer'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='remotezulipserver',
+            name='hostname',
+            field=models.CharField(max_length=128),
+        ),
+    ]

zilencer/models.py

@@ -12,7 +12,7 @@ class RemoteZulipServer(models.Model):
     uuid = models.CharField(max_length=36, unique=True)  # type: Text
     api_key = models.CharField(max_length=64)  # type: Text
 
-    hostname = models.CharField(max_length=128, unique=True)  # type: Text
+    hostname = models.CharField(max_length=128)  # type: Text
     contact_email = models.EmailField(blank=True, null=False)  # type: Text
     last_updated = models.DateTimeField('last updated', auto_now=True)  # type: datetime.datetime