Fix nondeterministic subscriptions for default test users.

Previously, the UserProfile objects were created in the order
generated by a Set, which meant tests would randomly start failing if
the code that runs before this part of populate_db changed (and thus
caused the Set object used to pass users into bulk_create_users to
have a different order when enumerated).

This fixes the issue in two ways -- one by sorting the users inside
bulk_create_users, and second by attaching subscriptions to users
based on a deterministic ordering.

zerver/lib/bulk_create.py

@@ -27,6 +27,7 @@ def bulk_create_users(realms, users_raw, bot=False):
             continue
         users.append((email, full_name, short_name, active))
         existing_users.add(email)
+    users = sorted(users)
 
     # Now create user_profiles
     profiles_to_create = []

zilencer/management/commands/populate_db.py

@@ -139,9 +139,12 @@ class Command(BaseCommand):
             create_streams(realms, zulip_realm, stream_list)
             recipient_streams = [Stream.objects.get(name=name, realm=zulip_realm).id for name in stream_list]
 
-            # Create subscriptions to streams
+            # Create subscriptions to streams.  The following
+            # algorithm will give each of the users a different but
+            # deterministic subset of the streams (given a fixed list
+            # of users).
             subscriptions_to_add = []
-            profiles = UserProfile.objects.select_related().all()
+            profiles = UserProfile.objects.select_related().all().order_by("email")
             for i, profile in enumerate(profiles):
                 # Subscribe to some streams.
                 for type_id in recipient_streams[:int(len(recipient_streams) *