Add default flavors during init-runonce

The nova team is removing the default flavors from a standard
deployment.  This is great for operators, who have to delete
the defaults anyways.  This patch adds the original default
flavors back during init-runonce so kolla users can be ready
to launch instances.

Closes-Bug: #1567964
Change-Id: I17daec98997a6e412a99f34d3f8a4324460d8c60