zpool import -d to specify device path

When we know which devices have the pool we are looking for, sometime
it's better if we can directly pass those device paths to zpool import
instead of letting it to search through all unrelated stuff, which might
take a lot of time if you have hundreds of disks.

This patch allows option -d <dev_path> to zpool import. You can have
multiple pairs of -d <dev_path>, and zpool import will only search
through those devices. For example:

    zpool import -d /dev/sda -d /dev/sdb

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chunwei Chen <david.chen@nutanix.com>
Closes #7077