When specifying raidz vdev name, parity count should match

When specifying the name of a RAIDZ vdev on the command line, it can be
specified as raidz-<vdevID> or raidzP-<vdevID>.
e.g. zpool clear poolname raidz-0 or zpool clear poolname raidz2-0

If the parity is specified in the vdev name, it should match the actual
parity of that RAIDZ vdev, otherwise the command should fail. This
commit makes it so.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Co-authored-by: Stuart Maybee <stuart.maybee@comcast.net>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
Closes #11742