Make all unit tests run on travis.ci

[dfsp-spirit]

Currently, not all test data is available on travis.ci and some tests are skipped there.

During development, we typically use only one python version when running the unit tests, so the skipped tests may fail under a different version.

We should find a method to make all test data available on travis.ci. The bash shell scipt that should do it (does it locally) does not seem to work on travis.ci for unknown reasons.