Illumos 5147 - zpool list -v should show individual disk capacity

The 'zpool list -v' command displays lots of info but excludes the
capacity of each disk. This should be added.

5147 zpool list -v should show individual disk capacity
Reviewed by: Adam Leventhal <adam.leventhal@delphix.com>
Reviewed by: Christopher Siden <christopher.siden@delphix.com>
Reviewed by: Matthew Ahrens <matthew.ahrens@delphix.com>
Reviewed by: Richard Elling <richard.elling@gmail.com>
Approved by: Dan McDonald <danmcd@omniti.com>

References:
  https://www.illumos.org/issues/5147
  https://github.com/illumos/illumos-gate/commit/7a09f97

Ported by: Turbo Fredriksson <turbo@bayour.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2688