MFC r324940:

Fix the error message when creating a zpool on a too-small device

Don't check for SPA_MINDEVSIZE in vdev_geom_attach when opening by path.
It's redundant with the check in vdev_open, and failing to attach here
results in the wrong error message being printed. However, still check for
it in some other situations:

• When opening by guids, so we don't get bogged down reading from slow devices like floppy drives.
• In vdev_geom_read_pool_label for the same reason, because we iterate over all providers.
• If the caller requests that we verify the guid, because then we'll have to read from the device before vdev_open verifies the size.

PR: 222227
Reported by: Marie Helene Kvello-Aune <marieheleneka@gmail.com>
Reviewed by: avg, mav
Sponsored by: Spectra Logic Corp
Differential Revision: https://reviews.freebsd.org/D12531