Add CentOS 7 environment setup instructions

This change adds instructions to Zuul From Scratch document
in order to prepare CentOS 7 system for Zuul and Nodepool
installation and configuration.

Steps to start/enable zookeeper service have been moved to distro
specific documents since the service name differs on distros.

Upcoming changes will add other sections such as installation
and configuration of Nodepool and Zuul.

Change-Id: Ie424a93d7e000d1e91801b45eb50173b58bc694e
Signed-off-by: Fatih Degirmenci <fdegir@gmail.com>

doc/source/admin/centos7_setup.rst

@@ -0,0 +1,65 @@
+:orphan:
+
+CentOS 7
+=========
+
+We're going to be using CentOS 7 on a cloud server for this installation.
+
+Prerequisites
+-------------
+
+- Port 9000 must be open and accessible from the internet so that
+  Github can communicate with the Zuul web service.
+
+Login to your environment
+-------------------------
+
+Since we'll be using a cloud image for CentOS 7, our login user will
+be ``centos`` which will also be the staging user for installation of
+Zuul and Nodepool.
+
+To get started, ssh to your machine as the ``centos`` user.
+
+.. code-block:: console
+
+   $ ssh centos@<ip_address>
+
+Environment Setup
+-----------------
+
+Certain packages needed for Zuul and Nodepool are not available in upstream
+CentOS 7 repositories so additional repositories need to be enabled.
+
+The repositories and the packages installed from those are listed below.
+
+* ius-release: python35u, python35u-pip, python35u-devel
+* bigtop: zookeeper
+
+.. code-block:: console
+
+   $ sudo yum update -y
+   $ sudo systemctl reboot
+   $ sudo yum install -y https://centos7.iuscommunity.org/ius-release.rpm
+   $ sudo yum install -y git python35u python35u-pip python35u-devel java-1.8.0-openjdk
+   $ sudo alternatives --install /usr/bin/python3 python3 /usr/bin/python3.5 10
+   $ sudo alternatives --install /usr/bin/pip3 pip3 /usr/bin/pip3.5 10
+   $ sudo pip3 install python-openstackclient bindep
+
+Install Zookeeper
+-----------------
+
+.. code-block:: console
+
+   $ sudo bash -c "cat << EOF > /etc/yum.repos.d/bigtop.repo
+   [bigtop]
+   name=Bigtop
+   enabled=1
+   gpgcheck=1
+   type=NONE
+   baseurl=http://repos.bigtop.apache.org/releases/1.2.1/centos/7/x86_64
+   gpgkey=https://dist.apache.org/repos/dist/release/bigtop/KEYS
+   EOF"
+   $ sudo yum install -y zookeeper zookeeper-server
+   $ sudo systemctl start zookeeper-server.service
+   $ sudo systemctl status zookeeper-server.service
+   $ sudo systemctl enable zookeeper-server.service

doc/source/admin/fedora27_setup.rst

@@ -39,3 +39,6 @@ Install Zookeeper
 
    sudo dnf install zookeeper -y
    sudo cp /etc/zookeeper/zoo_sample.cfg /etc/zookeeper/zoo.cfg
+   sudo systemctl start zookeeper.service
+   sudo systemctl status zookeeper.service
+   sudo systemctl enable zookeeper.service

doc/source/admin/zuul-from-scratch.rst

@@ -11,6 +11,7 @@ Environment Setup
 Follow the instructions below, depending on your server type.
 
   * :doc:`fedora27_setup`
+  * :doc:`centos7_setup`
 
 Installation
 ------------
@@ -65,18 +66,11 @@ further restrict public access.
 Starting Services
 -----------------
 
-Your system software management should have installed the Zookeeper service
-files for you.
-
-After you have Zuul and Nodepool installed and configured, you can start
-all of the services with::
+After you have Zookeeper, Nodepool, and Zuul installed and configured, you can
+start Nodepool and Zuul  services with::
 
    sudo systemctl daemon-reload
 
-   sudo systemctl start zookeeper.service
-   sudo systemctl status zookeeper.service
-   sudo systemctl enable zookeeper.service
-
    sudo systemctl start nodepool-launcher.service
    sudo systemctl status nodepool-launcher.service
    sudo systemctl enable nodepool-launcher.service