ci: Use a rootfs tarball for NFS root, instead of a ramdisk (for LAVA)

We anyway depend already on robust network support in the DUTs, and we
can save quite some time this way.

It will also allow us to grow further as we expand coverage.

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Reviewed-By: Rohan Garg <rohan.garg@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6114>
6 files changed