Illumos #3818

3818 zpool status -x should report pools with removed l2arc devices
Reviewed by: Saso Kiselkov <skiselkov.ml@gmail.com>
Reviewed by: George Wilson <gwilson@zfsmail.com>
Approved by: Christopher Siden <christopher.siden@delphix.com>

References:

https://www.illumos.org/issues/3818
illumos/illumos-gate@7f2416ef64fb43dab18d9b36c0da64bea37c0df3

Ported-by: Richard Yao <ryao@gentoo.org>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #1775