Comment 1 for bug 1562190

I was able to reproduce this on my own as well. There are more than just instances and networks being orphaned here. You also have volumes, glance images, and essentially everything that can be assigned to a project.

I propose that keystone checks the tenants to see if there are any resources available in them. One idea would be to scan the database (i.e. select * from instances where project_id='tenant' and deleted=0;) if any of these select commands return an active resource keystone should send an error to the user both via Horizon and CLI that they need to delete the available resources or migrate them before deleting a tenant.