Merge lp://qastaging/~dobey/ubuntu-app-launch/throw-less into lp://qastaging/ubuntu-app-launch/16.10

Add a try/catch inside the for loop in ::list().

For some reason the Libertine back-end was the only one not doing this. This adds a try/catch inside the for loop for listing installed apps, as relying on the application using the API to handle exceptions from here still results in a broken listing of apps, as the loop would never complete when an exception was thrown. So we need to log and continue on, as the other back-ends do, here.