Illumos #3397, #3398

3397 zdb <pool> <objnum> output is too verbose
3398 zdb can't dump feature flags zap objects

Reviewed by: Matt Ahrens <matthew.ahrens@delphix.com>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed by: Dan Kimmel <dan.kimmel@delphix.com>
Reviewed by: Eric Schrock <eric.schrock@delphix.com>
Reviewed by: Richard Lowe <richlowe@richlowe.net>
Approved by: Dan McDonald <danmcd@nexenta.com>

References:
  illumos/illumos-gate@e690fb27a7d1483f052505e1ff373d205f9dee99
  https://www.illumos.org/issues/3397
  https://www.illumos.org/issues/3398

Ported-by: Brian Behlendorf <behlendorf1@llnl.gov>