MFV r262570:

4626 libzfs memleak in zpool_in_use()

illumos/illumos-gate@fb13f48f1d9593453b94cd1c7277553b56f493c8

MFC after:	2 weeks

git-svn-id: svn+ssh://svn.freebsd.org/base/head@262577 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
(cherry picked from commit 870eee61e5b9d4b2371792dc96b2cb6ed8f666bf)