Import discovery-ironic element from upstream DIB review

Imported patchset 11 of https://review.openstack.org/#/c/107672/
Enable building of discovery-ironic ramdisk in instack-build-images
Updated discovery-ironic with fixes after Gerrit review

Imported patchset 1 of https://review.openstack.org/#/c/122151/
Load discovery image into Glance
Merge pull request #17 from Divius/master

Support Ironic hardware discovery