Reconsider policy of skipping tests

Currently we can skip tests in testsuite if dependent applications are not installed. That may have the effect that when new images are added in the CI, or during the rebuild of new images some components no longer get included, we will not detect the testing regression. As such I'd like to propose to not skip tests on missing applications, but rather to make them configurable via configure.ac.

We could also differentiate the policy between

• tests/suite (which is run only during CI)
• tests/ (which is run on installed systems and CI)