avocado.test: If main test action fails, cleanup still needs to be executed

This was quite the brown paper bag bug I made: If the
main action fails, we need to call cleanup() no matter
what.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
selftests/functional: Verify that cleanup is called on action failure

So we don't incur in the bug we just fixed.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
Merge pull request #88 from avocado-framework/fix-cleanup

avocado.test: If main test action fails, cleanup still needs to be execu...