Write client tests for ivi_application

There is currently no test coverage for the client side implementation of ivi_application.

Write ivi_application specific tests, or (if possible) ensure existing tests are run on ivi_application as well.

ivi_application is a small and simple protocol, but we occasionally experience regressions there as well. It should be simple to write these tests, once a good approach for testing shell extension specific testing has been found.