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

I'm still not convinced about having expectations in the "before" block. I would have done it in an alternative way that looks unnecessarily verbose (even redundant) but I still feel is more correct from a RSpec point of view. I would really like to know what others think.

```ruby
describe "#restart_service" do

  context "when remote administration is being enabled" do
    before(:each) do
      Remote.Enable()
      allow(Service).to receive(:active?).with("display-manager").and_return(active_display_manager)
    end

    context "when display-manager service is active" do
      let(:active_display_manager) { true }

      it "adjusts needed services and warns the user" do
        allow(SystemdTarget).to receive(:set_default)

        expect(Service).to receive(:Reload).with("display-manager").and_return(true)
        expect(Service).to receive(:Restart).with("xinetd").and_return(true)
        expect(Report).to receive(:Warning)
        Remote.restart_service
      end

      it "sets default systemd target" do
        allow(Service).to receive(:Reload)
        allow(Service).to receive(:Restart)
        allow(Report).to receive(:Warning)

        expect(SystemdTarget).to receive(:set_default).with("graphical").and_return(true)
        Remote.restart_service
      end
    end

    context "when display-manager service is inactive" do
      let(:active_display_manager) { false }

      it "adjusts needed services" do
        allow(SystemdTarget).to receive(:set_default)

        expect(Service).to receive(:Restart).with("display-manager").and_return(true)
        expect(Service).to receive(:Restart).with("xinetd").and_return(true)
        Remote.restart_service
      end

      it "sets default systemd target" do
        allow(Service).to receive(:Restart)

        expect(SystemdTarget).to receive(:set_default).with("graphical").and_return(true)
        Remote.restart_service
      end
    end
  end
end
```