Fix import finding spare/l2cache when path changes

Fix import finding spare/l2cache when path changes

When spare or l2cache device path changes, zpool import will not fix up
their paths like normal vdev. The issue is that when you supply a pool
name argument to zpool import, it will use it to filter out device which
doesn't have the pool name in the label. Since spare and l2cache device
never have that in the label, they'll always get filtered out.

We fix this by making sure we never filter out a spare or l2cache
device.

Reviewed by: Richard Elling <Richard.Elling@RichardElling.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Chunwei Chen <david.chen@osnexus.com>
Closes #6158