Fix public activity showing private repos (#892)

* Fix public activity showing private repos (#811)

Signed-off-by: Morgan Bazalgette <the@howl.moe>

* error check after setting is_private to true

* Add test for UpdateRepository w/ visibility change

models/fixtures/user.yml

@@ -149,3 +149,18 @@
   avatar_email: user10@example.com
   num_repos: 3
   is_active: true
+
+-
+  id: 11
+  lower_name: user11
+  name: user11
+  full_name: User Eleven
+  email: user11@example.com
+  passwd: password
+  type: 0 # individual
+  salt: salt
+  is_admin: false
+  avatar: avatar11
+  avatar_email: user11@example.com
+  num_repos: 1
+  is_active: true