Fixes #8317 - Implement Reboot action

I think this method should always explicitly return `true`. Because when this is triggered from orchestration (`setReboot`) then return value matters. When `false` orchestration fails and everything falls down.

Now the question is if we want to return `false` on failure and I say we should not. Host that does not reboot is not fatal error IMHO, administrator can easily fix this by rebooting it and provisioning will continue. Opinions?

If we agree, I tend to add a flash error message to the `managed_extensions.rb#setreboot` method. We don't need to show anything on succes, but on error administrator will not notice that the host was not rebooted. Actually you can see the progress bar changes the color from green to red but its just fraction of second and then everything seems to be nice but you can only see the error message in the log (and the host is not rebooting). I think a red flash would be good option here.