tuned: Rework logic to gracefully handle the service starting

[SludgeGirl]

Previously starting the service would lead to a server disconnected message, these changes allow us to instead fully wait until the service has started before showing the profile selection, meaning we no longer encounter that error

[martinpitt]

Hello @SludgeGirl !

Previously starting the service would lead to a server disconnected message

This sounds like a bug in tuned? The card already explicitly starts tuned.service before trying to talk to it. Once the service is running, it must be ready to accept D-Bus calls, otherwise there's nothing (other than repeatedly trying) that can be done on the caller side. But "server disconnected" often happens when the service crashes. Do you have some details about that? Can that be observed with running the tests against the tumbleweed image?

This PR introduces a lot of extra UI (a whole dialog, etc) but doesn't really address the race other than by "slowing down" the user.

I'd like to first understand what's going on. Thanks!

[SludgeGirl]

Hey @martinpitt!!

Alright so, I've had another dig through just to refresh myself (sorry for the wait). There's a couple things this aimed to handle

First is that the current behavior feels undefined and unexpected. From everything I've seen of cockpit so far, it's very explicit and asks permission for every action it wants to do that's extra from the intended user action, this is a stance I have alot of respect for. Clicking "performance: None" isn't clear that it would start tuned. The extra dialog I've added aimed to make this clearer along with helping to handle the issue (Sorry I forgot to make this clear in my initial explanation)

In terms of the technical issue, let me prefix this by saying please let me know if anything I say doesn't make sense or is wrong. I've done my best here but with all the react state changes, systemd service status changes and dbus then everything changing alot through it's execution, it's been a nightmare to try and get my head around.

But I believe as this executes and we start tuned inside the dialog, the some of the references like poll, and tunedDbus don't get updated inside the dialog because it's not re-rendered:

cockpit/pkg/systemd/overview-cards/tuned-dialog.jsx

Lines 127 to 132 in 626b74c

	const TunedDialog = ({
	updateButton,
	poll,
	tunedDbus,
	tunedService,
	}) => {

So when we then go to call those once the service.start promise returns we fail and return back the error because the dbus object is disconnected but is still used in poll during that point of the execution:

cockpit/pkg/systemd/overview-cards/tuned-dialog.jsx

Lines 269 to 273 in 626b74c

	tunedService.start()
	.then(updateButton)
	.then(withTuned)
	.catch(setError)
	.finally(() => setLoading(false));