Relax integration tests a bit

Currently all the integration tests check for identical build results instead of only checking the specific features they are testing.

This means that in any case where output has intentionally changed, for instance as a result of now compressing all debugging information which recently landed; all the integration tests need to be tediously updated.

This seems wrong, for instance the point of the compose tests is for testing the split-rules and how the compose element leverages that, and the features that the compose element provides; which is all a matter of which file was included or excluded, and where the file lands.

It would be much better if lib.sh provided some convenience functions for testing certain things in the results, like the existence of files, their permissions, and sometimes their content - and that the test cases being run use these individual functions to only test the things that are relevant to the test case.