[docs] Section 'Install the Fuel Master node' refers to unreleased Fuel 10 and miss Centos version

There is a Fuel Master Node installation guide:
http://docs.openstack.org/developer/fuel-docs/userdocs/fuel-install-guide/install/install_install_fuel_master_node.html

which:
a) suggests an alternate installation method - from RPM packages
b) reffers to under-development Fuel 10 version:
Quote: "sudo rpm -i http://packages.fuel-infra.org/repositories/centos/master-centos7/os/x86_64/Packages/fuel-release-10.0.0-1.mos6376.git.a8c98d0.noarch.rpm"

We have only Fuel 9.1 as stable version for this time.
c) Does not specify precisely that Centos 7.2 is needed (customer tried to use Centos 7.1 and it failed)
Quote: "Install CentOS 7 on the node you assume to be the Fuel Master node as described in the official CentOS documentation".

At the same time guides for 9.0 and 9.1 placed on docs.mirantis.com do not suggest any other alternate installation method for Fuel Master. Only ISO usage is proposed:

https://docs.mirantis.com/openstack/fuel/fuel-9.1/quickstart-guide/qs-install-fuel.html