Wait for the "state" property to change as well as the "state-reason".
We only update the UI when the former arrives, but the test was working
correctly on faster machines, making it difficult to pinpoint.
Closes: #1768
This adds tests for the network panel based on the test service found in
NetworkManager. Another possible solution may be to use the one from
dbusmock, however NetworkManager already has readily available code to
write tests in C which makes checking the widget hierarchy easier.
