Make test step run tests depending on which modules/files where changed

[casparvl]

Currently, the test step runs all tests tagged with -t CI -t '1_node|2_nodes'. To save time, we'll limit it to only running the OSU tests for now through this PR. However, long term, we would want the right tests to be run for the right changes.

E.g.

• If GROMACs was built, we want to run the GROMACS tests (call ReFrame with -n GROMACS)
• If OpenMPI was built, we want to run e.g. OSU and at least one OpenMPI-based end-user application (e.g. -n OSU -n GROMACS.*foss)

That requires two things:

1. We need to be able to identify what has changed
2. We need a mapping between what has changed, and what should be tested

To achieve (1) the easiest is maybe to check the tarball contents. Extracting module names from that should be pretty straightforward. We should also figure out what tests to run for other changes, e.g. a change to the init script.

To achieve (2), we should pick some easy format (yaml?). I'd probably create seperate files for mapping changes to modules and mapping other changes. E.g.

# module_test_mapping.yml
GROMACS:
    GROMACS
OpenMPI:
    OSU
    GROMACS

and

# other_test_mapping.yml
init/bash:
    OSU
scripts/gpu_support:
    OSU.*CUDA

What I don't know is how YAML treats slashes, and other regex characters (the values should be regex patterns, as there are accepted by the -n argument of ReFrame).