Follow up Secure boot support for irmc-pxe driver.
Follow up Secure boot support for irmc-pxe driver.

This commit makes changes based upon review feedback
in Ie82ff07421d23b5c0d26e2d2fbde33fc9f8e3c42.
- Updates doc string: remove redundant sentence
- Updates operation string

Change-Id: I929cf7022a7a27f3bf763c8e9c7dc3ef91326882

openstack/ironic,openstack/ironic