Display chroot names and details

Add option '-a' to operate on all chroots and '-l' to list croutonversion details.
This won't work properly in the presence of spaces, and needs to filter out junk files.  The cleanest way I can think of right now is this:

```
for NAME in "$CHROOTS"/*; do
    if [ -d "$NAME" ]; then
        set -- "$@" "${NAME##*/}"
    fi
done