bare-metal can reboot boards into an existing rootfs on intermittent
device failure, but traces-db doesn't do any sanity-checking of the local
downloads of traces and would proceed to just trying to replay them.
Nuke any existing trace db so that it re-downloads every time, same as
LAVA or docker container tests do.
Fixes: #5585
Reviewed-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/15440>