Use the correct state name for unavailable pools in zpool list

This corrects inconsitencies between zpool list and zpool status which are
both described as displaying the pool <state> however zpool list would use
this hardcoded FAULTED instead of the correct UNAVAIL.

MFC after:	1 month


git-svn-id: svn+ssh://svn.freebsd.org/base/head@276446 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f