Description of problem:

* There is a swift container for the overcloud which contains:
    * rendered heat templates for the overcloud deployment
    * autogenerated passwords and every heat parameter we pass
    * Private keys.

* It can be fetched with:
    openstack container list
    mkdir <somewhere to put the container>
    cd <somewhere to put the container>
    openstack container save <container name>
        e.g. openstack container save overcloud

This data -- and any other sensitive data in the undercloud swift containers should be encrypted at rest.  Much of the work to encrypt swift containers is already completed.

For example, here is a set of patches which enable swift encryption using barbican in the undercloud.

https://review.openstack.org/#/q/topic:secret-management+(status:open+OR+status:merged)