Flaky tests/auto/dbus/qdbusconnection_spyhook is timing out on Linux

DBus test is causing trouble in CI by timing out periodically on Linux VMs:

https://testresults.qt.io/coin/integration/qt/qtbase/tasks/1553102874

https://testresults.qt.io/coin/integration/qt/qtbase/tasks/1553060244

Flaky failures typically get re-staged multiple times slowing down development so it would be beneficial for everyone to either fix the test or blacklist it.

I managed to reproduce the error quite easily on RHEL 7.4 debug vm with

cd tests/auto/dbus/qdbusconnection_spyhook
qmake && make
while true; do ./target_wrapper.sh ./tst_qdbusconnection_spyhook connectToPeer -maxwarnings 0; done

After couple of iterations the test will hang on tst_QDBusConnection_SpyHook::initTestCase()