Prepare the target hosts in openstack-ansible

[Fabien Magagnosc]

- [X] This doc is inaccurate in this way: on CentOS 7, the settings "kernel.printk" is actually not supported/existing for the Linux kernel 3.10.X, and cause the sensible to failed, as this return an error during host kernel changes and try to apply them, as this failed during the sysctl -p /etc/sysctl.conf execution done after all the settings are applied (see below)

[root@host01 openstack-ansible]# echo "kernel.printk='4 1 7 4'" >> /etc/sysctl.conf
[root@host01 openstack-ansible]# sysctl -p /etc/sysctl.conf
sysctl: setting key "kernel.printk": Invalid argument
kernel.printk = '4 1 7 4'
sysctl: setting key "kernel.printk": Invalid argument
kernel.printk = '4 1 7 4'

- [ ] 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: on 2019-08-15 14:54:55.656216
SHA: 2466e0dfcddb829b3fdb8f1252e04277db89f4ed
Source: https://git.openstack.org/cgit/openstack/openstack-ansible/tree/deploy-guide/source/targethosts.rst
URL: https://docs.openstack.org/project-deploy-guide/openstack-ansible/stein/targethosts.html