vct/server: Implemented Feature #200: Allow user-provided overlay for sliver
Save ssl certs too on sysupgrade, use keep.d instead of $TO_SAVE
Touch files to save when using overlay, small fixes
confine/lxc: mount sliver/confine directory readlony with node-id and slice-id files
confine: link busybox-static into sliver /confine directory if it exists
confine: empty sliver overlay with given size
lxc/confine: tar-extract experiment data with --no-overwrite-dir to sliver rootfs
Add INSTALL_BIN for confine.remote-upgrade
Merge branch 'testing'