Fixes #8317 - Implement Reboot action

Hmmm what if we don't do that as a concern? Simple helper class in the lib/ folder would work, rails should autoload it I believe. This really looks ugly and I can't tell how to do this nicer. Maybe @GregSutcliffe knows better...

To give you the context, Ori is adding new Reboot button which is useful for testing images. The API is there, why not to have the button :-) We want to generalize the method so controllers can use it.