The linux kernel is not reproducible because the build user
and domain is included into the kernel. Set the build user
to `builder` and build domain to buildhost.
It's also possible to build reproducible builds by setting
KERNEL_BUILD_USER KERNEL_BUILD_DOMAIN to static values.
Signed-off-by: Alexander Couzens <lynxis@fe80.eu>
(cherry picked from commit fdd0a8d49118134070c13231b6d10ec88b9105da)