Driver merge review comments from 111425-2-3

This review contain fixes that addresses the review comments
raised in https://review.openstack.org/#/c/111425 revisions 2 & 3.
Once these changes are merged here in Ironic, they will be
proposed as updates to the patch series over in Nova.

Change-Id: Ie7bc50a9804373c9c4f8850f4e2b201c1d01effb
Merge "Driver merge review comments from 111425-2-3"