ctest: show test output in case of failures

ctest: show test output in case of failures

ctest as run by cmake by default does not show the output of the tests
even if the tests failed. In terms of our tests it could be handy to set
it always, but unfortunately it seems like cmake doesn't allow it if the
internet is to be believed, so lets enable it at least while building
packages and on travis.

Gbp-Dch: Ignore