Install and configure for Red Hat Enterprise Linux and CentOS miss several steps

[miaoyuliang]

there missing several steps while install designate in https://docs.openstack.org/designate/latest/install/install-rdo.html

though in the page of https://bugs.launchpad.net/designate/+bug/1603808 have some steps to solve it, but it is not enough for rdo-installation

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:

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

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-----------------------------------
Release: 7.0.0.0b3.dev9 on 2018-06-18 06:35
SHA: fe60c5b11e4952bb8578fb817e4fc42015b7aad0
Source: https://git.openstack.org/cgit/openstack/designate/tree/doc/source/install/install-rdo.rst
URL: https://docs.openstack.org/designate/latest/install/install-rdo.html

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/576690

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/576694

[OpenStack Infra (hudson-openstack)]

Change abandoned by miaoyuliang (<email address hidden>) on branch: master
Review: https://review.openstack.org/576690
Reason: repeated submit

[OpenStack Infra (hudson-openstack)]

Change abandoned by miaoyuliang (<email address hidden>) on branch: master
Review: https://review.opendev.org/576694