Display chroot names and details

Add option '-a' to operate on all chroots and '-l' to list croutonversion details.
The output here should be done on stdout so it can be filtered reasonably.  Don't use error; instead echo normally with the chroot list on its own line and then exit 0.  I'm not actually sure we need the header, either.  Just printing out the list without any fanciness would be more useful for scripting.