Configuration of remote administration has been fixed to reload/restart services and/or warn user if necessary

- bnc#893606
- According to the bugreport, Yast Runlevel just restarts display manager while it enables remote administration
- I've fixed the behavior in a way that it starts or reloads services as much as possible and if the display manager is already running, Yast warns user to restart it manually or log out and log in again
- Includes a  nice test case

You could even save the "before" in both contexts (active and inactive display-manager) having just one allow in the "before" block of the outer context and using ```let```.

Hmmm... better explained with a code chunk.
```
describe "#restart_service" do
  before do
    allow(Service).to receive(:active?).with("display-manager").and_return(active_display_manager)
  end

  context "when remote administration is being enabled" do
    before(:each) do
      Remote.Enable()
    end

    context "when display-manager service is active" do
      let(:active_display_manager) {true}

      it "adjusts needed services and warns the user" do
        expect(Service).to receive(:Reload).with("display-manager").and_return(true)
        expect(Report).to receive(:Warning)
        Remote.restart_service
      end
    end
  end
end