Install and configure for Red Hat Enterprise Linux and CentOS in freezer

[Father Vlasie]

This bug tracker is for errors with the documentation, use the following as a template and remove or add fields as you see fit. Convert [ ] into [x] to check boxes:

- [x] This doc is inaccurate in this way: ______

This command assumes there is a "service" project which may not be the case:

     $ openstack role add --project service --user freezer admin

Perhaps a note should be added to let people know they may need to change it.

- [ ] This is a doc addition request.
- [ ] I have a fix to the document that I can paste below including example: input and output.

If you have a troubleshooting or support issue, use the following resources:

 - Ask OpenStack: http://ask.openstack.org
 - The mailing list: http://lists.openstack.org
 - IRC: 'openstack' channel on Freenode

-----------------------------------
Release: 7.0.0.0b2.dev8 on 2018-04-26 13:23
SHA: 1ebd6d12efb78bbaac0ba454ab03d52659dddfde
Source: https://git.openstack.org/cgit/openstack/freezer/tree/doc/source/install/install-rdo.rst
URL: https://docs.openstack.org/freezer/latest/install/install-rdo.html