Switch is_scratch default to True

The value is properly set by triggers only for brew pipelines, but the default is applied for every pipeline. Thus, kpet thinks this setting applies to every kernel we build (i.e. not from brew), which is not what we want. As a result, we have been adding the "officialbuild" kpet component for every RHEL kernel which may have resulted in picking up tests that should not have been picked.

Signed-off-by: Veronika Kabatova vkabatov@redhat.com