Add CKPOINT, EXPANDSZ, and FRAG columns to all zpool list examples in the handbook

[bcr]

Summary

This updates all headers in the zpool list examples in the ZFS chapter of the FreeBSD handbook to display all columns currently shown. In particular, CKPOINT, EXPANDSZ, and FRAG were added and set with sensible defaults for the example.

Test Plan

1. Apply the patch to the doc tree
2. Build the handbook
3. View the output
4. Make comments or Approve ;-)

[sevan]

1. looked at the raw diff
2. checked the build status in this review
3. confirmed the zpool list output locally
4. approved :)

[bcr]

@sevan: Haha, excellent. ;-) I shall proceed to commit.