Multiple Regions Deployment with Kolla in kolla-ansible

- [X] This doc is inaccurate in this way:
- [X] This is a doc addition request:

Documentation related to multiple regions deployment with kolla-ansible misses to precise that passwords from /etc/kolla/passwords.yml on RegionOne should be shared among the other regions. Also, it must be specified if all the passwords should be shared or just a subset.

Finally, it is necessary to evaluate the related security risks as well as the precautions to be taken to mitigate them (For example in the case of a wide area network deployment (such as NFV))

PS: In our multiple region setup we copied the whole /etc/kolla/passwords.yml to the second region in order to make it work.

Thanks in advance

-----------------------------------
Release: 8.1.0.dev530 on 2019-07-18 10:53:04
SHA: c6d0733b9dee1f2e562271149ce46f6ddc1abd40
Source: https://opendev.org/openstack/kolla-ansible/src/doc/source/user/multi-regions.rst
URL: https://docs.openstack.org/kolla-ansible/latest/user/multi-regions.html