Support for non-Glance image references
Support for non-Glance image references

Add the ability to provide non-Glance references for images that are
used by Ironic.

Change-Id: I7e3e27250053260142c2633f1bcc49ffdf5176c1

NaohiroTamura/ironic-specs,openstack/ironic-specs,naterh/ironic-specs,bcornec/ironic-specs