kunit: kunit_tool: Fix invalid result when build fails

kunit: kunit_tool: Fix invalid result when build fails

When separating out different phases of running tests[1]
(build/exec/parse/etc), the format of the KunitResult tuple changed
(adding an elapsed_time variable). This is not populated during a build
failure, causing kunit.py to crash.

This fixes [1] to probably populate the result variable, causing a
failing build to be reported properly.

[1]:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=a0732ca1b9592f649051396193f8251707152c42

Signed-off-by: David Gow <davidgow@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Tested-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>