As per https://github.com/mitchellh/packer/issues/1142, it's critical to add openstack_provider: rackspace in order to get anything to work reliably with Rackspace and Packer in 6.0.
Question: should the openstack_provider field now be marked as required?
Add configuration option `networks`, a list of network UUIDs, to attach to the
source instance.
In some openstack installs, no default network will be attached or the network
with the ability to attach a public floating IP will need to be specified.
If `openstack_provider:rackspace` is omitted in the configuration, the example
won't work at all against rackspace. Not sure what the actual documentation for
this configuration value should be, but this was a major source of irritation
when I couldn't get the default example working against Rackspace.
