MFC r333630: Fix 'zpool create -t <tempname>'

MFC r333630: Fix 'zpool create -t <tempname>'

Creating a pool with a temporary name fails when we also specify custom
dataset properties: this is because we mistakenly call
zfs_set_prop_nvlist() on the "real" pool name which, as expected,
cannot be found because the SPA is present in the namespace with the
temporary name.

git-svn-id: svn://svn.freebsd.org/base/stable/10@335546 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f