> In OpenStack, it's simply a UUID right? 

Actually No. In Keystone in openstack, the format of project_id is 32-character hex string (that happens to be generated from uuid.uuid4(), then dashes chopped off). 

So, we want to make sure that the tenant_id specified in our CLI looks like a keystone's tenant id, which is not exactly a UUID, but just 32 hex characters.