On first boot, HomeScreen sometimes starts without apps being ready

This issue appears to occur only on first boot. Sometimes HomeScreen will start, but there will be no icons because the apps are not yet initialized. If you then do:

systemctl restart user@

Then HomeScreen will restart with the apps visible.

Given that this occurs only on first boot, I'm guessing it is caused by some race condition between agl-postinsts and HomeScreen.service, and then we need to explicitly mark some dependency.

I've noticed that this issue appears to reproduce better using Qt 5.8. I'm guessing Qt 5.8 exposes some race condition that was previously hidden, due to timing differences.

To reproduce, just build qemux86-64 with this branch for meta-agl-demo:

sandbox/mkelly/qt58

And this branch for meta-qt5:

github/master

commit 5f837b4

If it doesn't immediately reproduce, also try doing runqemu with kvm, as it will change the timing.