[umt] Just print out the error message rather than crafting a new message and raising another exception.

Signed-off-by: Brad Figg <brad.figg@canonical.com>
[umt] Make sure the kernel-test-results directory exists on the SUT before running the tests.

Signed-off-by: Brad Figg <brad.figg@canonical.com>
[umt.cfg.example] cleanup

Signed-off-by: Brad Figg <brad.figg@canonical.com>