emit permission denied error if unprivileged user attempts zpool import

[ashfixit_gmail.com]

Summary

Buglet fix from openzfs hackathon: zpool import without sudo has misleading error

Extend condition check for emitting permission denied error.

Test Plan

before (incorrect behaviour)

zpool import fred

cannot import 'fred': no such pool available

after( corrected )

/usr/obj/usr/12headsrc/amd64.amd64/cddl/sbin/zpool/zpool import asdf

cannot discover pools: permission denied
Exit 1