Fix to Ironic gate job's baremetal config change

Fix to Ironic gate job's config change that clears out baremetal
configs, switched to {} rather than blank string in order to avoid
os-apply-config issue with key search through strings.
(https://bugs.launchpad.net/os-apply-config/+bug/1321827)

Unblocks: openstack/tripleo-image-elements commit #
          https://review.openstack.org/88340

Change-Id: I9319c0b4024b68ab46a2cd02ddf259a7a713433a
Merge "Fix to Ironic gate job's baremetal config change"