contrib/rootfs-builder: add /proc, /dev, /sys in rootfs
contrib/rootfs-builder: add /proc, /dev, /sys in rootfs

The rootfs needs to have /proc, /dev, /sys pre-created because the
runtime might not be able to create those, specially in user namespaces.

Signed-off-by: Alban Crequy <alban@kinvolk.io>

And sort them alphabetically.

Signed-off-by: W. Trevor King <f75897670c17327c42ab201733fb8a81ff9f4c34@tremily.us>

wking/ocitools-v2,opencontainers/ocitools,liangchenye/ocitools,opencontainers/runtime-tools,liangchenye/ocitools,wking/ocitools-v2,opencontainers/runtime-tools,opencontainers/ocitools