zpool reopen should detect expanded devices

zpool reopen should detect expanded devices

Update bdev_capacity to have wholedisk vdevs query the
size of the underlying block device (correcting for the size
of the efi parition and partition alignment) and therefore detect
expanded space.

Correct vdev_get_stats_ex so that the expandsize is aligned
to metaslab size and new space is only reported if it is large
enough for a new metaslab.

Reviewed by: Don Brady <don.brady@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed by: George Wilson <george.wilson@delphix.com>
Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed by: John Wren Kennedy <jwk404@gmail.com>
Signed-off-by: sara hartse <sara.hartse@delphix.com>
External-issue: LX-165
Closes #7546
Issue #7582