kunit: tool: fix broken default args in unit tests

Commit ddbd60c7 ("kunit: use --build_dir=.kunit as default") changed
the default build directory for KUnit tests, but failed to update
associated unit tests for kunit_tool, so update them.

Fixes: ddbd60c7 ("kunit: use --build_dir=.kunit as default")
Signed-off-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>