Enhance the offline tests

This adds new offline tests:

- checks that files generated by hspace can be read by hbal/hinfo
- checks that hbal handles node groups as expected
- checks that enabling multiple backends results in failure
- checks hspace machine readable code and higher verbosity
- enables a "FAIL" message on error exit

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>