By default, build outside of Drone works the same and builds only amd64
version, loads images back into dockerd, etc.
If multiple platforms are used, multi-arch images are built which can't
be exported to docker or to `.tar` image, they're always pushed to the
registry (even for PR builds to our internal CI registry).
Artifacts as files (initramfs, kernel) now have `-arch` suffix:
`vmlinuz-amd64`, `initramfs-amd64.xz`. "Magic" script normalizes output
paths depending on whether single platform or multiple platforms were
given.
VM provisioners accept magic `${ARCH}` in initramfs/kernel paths which
gets replaced by cluster architecture.
Signed-off-by: Andrey Smirnov <smirnov.andrey@gmail.com>
