This allows us to set parameters for server boot on various images.
This is the equivalent of the "--property" flag when using "openstack
server create". Various tools on the booted servers can then query
the config-drive metadata to get this value.
Needed-By: https://review.openstack.org/604193/
Change-Id: I99c1980f089aa2971ba728b77adfc6f4200e0b77
7015bd9af4