devel/py-libzfs: Unbreak FreeBSD <13.1

Commits in the previous update fixed incorrect zpool status
handling, but broke the build for older versions of ZFS.

Now, zpool_status_t enumerators are checked at configure time.
This fixes the build for all supported FreeBSD releases and fixes
the incorrect zpool status handling.

• Check zpool_status_t enumerators at configure time
• Fix round-tripping ZFSException through pickle
• Remove zpool_get_physpath

Approved by: lwhsu (implicit)
Sponsored by: iXsystems, Inc.