Merge branch 'rs-test-seed' into 'master'

Don't disable the Rails mailer when seeding the test environment

See merge request gitlab-org/gitlab-ce!15690

lib/gitlab/seeder.rb

@@ -8,7 +8,8 @@ end
 module Gitlab
   class Seeder
     def self.quiet
-      mute_mailer
+      mute_mailer unless Rails.env.test?
+
       SeedFu.quiet = true
 
       yield