Cannot create new machine with compute image without boot volume

[vwbusguy]

When attempting to use a compute flavor (as listed), the provision fails with message, "Policy doesn't allow compute_flavor:create:image_backed to be performed."

Compute images require a boot to volume rather than local. See https://github.com/chef/knife-rackspace/issues/91

It appears fog supports booting to a volume, but I don't see that option from the vagrant-rackspace plugin documentation.

[vwbusguy]

It looks like this is the preferred method for compute images, which require a volume to boot: https://developer.rackspace.com/docs/cloud-servers/v2/api-reference/svr-basic-operations/#post-create-bootable-volume-and-server-servers