populate_db: Don't restrict email domains by default in tests and dev.

The email domain restriction to @zulip.com is annoying in development
environment when trying to test sign up. For consistency, it's best to
have tests use the same default, and the tests that require domain
restriction can be adjusted to set that configuration up for themselves
explicitly.

zerver/tests/test_users.py

@@ -617,6 +617,7 @@ class AdminCreateUserTest(ZulipTestCase):
         ))
         self.assert_json_error(result, "Bad name or username")
 
+        do_set_realm_property(realm, 'emails_restricted_to_domains', True)
         result = self.client_post("/json/users", dict(
             email='romeo@not-zulip.com',
             password='xxxx',