Bug 1105660 - ActiveModel::Obserservs moved out from rails > 4.0

Bug 1105660
Bugzilla link <https://bugzilla.redhat.com/show_bug.cgi?id=1105660>
From rails > 4.0, ActiveModel::Observers has moved out as a gem
`rails-observers` <https://github.com/rails/rails-observers>.
And having a project using rails > 4.0 will broke the `ctl_app`.