test: detect finished install via DEVICE_TRAY_MOVED event

The old images code would auto-reboot after an ISO install so
the test code triggered on qmp:RESET. However with the change
to not auto-reboot [0] this is no longer feasible and we
need to detect `DEVICE_TRAY_MOVED` events that are emited
when kickstart calls `halt --eject`.

[0] osbuild#230

test/test_build.py

@@ -442,7 +442,8 @@ def test_iso_installs(image_type):
         fp.truncate(10_1000_1000_1000)
     # install to test disk
     with QEMU(test_disk_path, cdrom=installer_iso_path) as vm:
-        vm.start(wait_event="qmp:RESET", snapshot=False, use_ovmf=True)
+        vm.start(wait_event="qmp:DEVICE_TRAY_MOVED", snapshot=False, use_ovmf=True)
+        vm.run("sync", user="root", keyfile=image_type.ssh_keyfile_private_path)
         vm.force_stop()
     # boot test disk and do extremly simple check
     with QEMU(test_disk_path) as vm: