ci/init-stage1: avoid duplicate mounts

Check if filesystems are mounted before attempting to mount them,
and use mkdir -p to prevent errors if directories already exist.

Signed-off-by: Vignesh Raman <vignesh.raman@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/35961>
1 file changed