[upstream] Add steps to checkout/configure/run DevStack

The Demo Environment slides have an exercise to make sure that
DevStack is checked out to the VM where they wish to run DevStack
but have no instructions for doing so.  I added a slide with the
steps for cloning, configuring and running devstack.

I also improved the wording of the exercise on the final slide.
The details on the slide for using 'screen' were pretty light so
I also added content there.

Change-Id: I96a623323020a630d88d5f6d8659a6d49bd44ec7

doc/upstream-training/source/slides/code-devstack.rst

@@ -23,18 +23,49 @@ DevStack
 
 - Documentation: http://docs.openstack.org/developer/devstack/
 
+DevStack Clone and Setup
+========================
+- Clone DevStack to your vm
+
+.. code-block:: console
+
+  git clone https://github.com/openstack-dev/devstack
+
+- Make any local configurations changes (set passwords, IP addresses, etc.)
+
+.. code-block:: console
+
+  cd ./devstack
+  cp ./samples/local.conf .
+  vi ./local.conf
+
+- Run DevStack
+
+.. code-block:: console
+
+  ./stack.sh
+
+.. note::
+
+  - DevStack should already be installed in the VM image you downloaded.
+    These instructions are provided for future reference in the case that
+    students need to start from scratch.
+
 http://localhost/
 =================
 
+- After DevStack is run Horizon is accessible via localhost
+
 .. image:: ./_assets/devstack-http-localhost.png
   :width: 100%
 
-Service terminals
-=================
+Using Linux 'screen'
+====================
 
-- Using Linux 'screen'
 - Access the terminals the installed services are running in
-- Use command 'screen -x' to see the running services
+- Use command 'screen -ls' to see the running screen sessions
+- Use command 'screen -R <session name>' or 'screen -C stack-screenrc' to
+  attach to or start a new session
 - For further commands see the
   `User's Manual <https://www.gnu.org/software/screen/manual/screen.html>`_
 
@@ -45,5 +76,24 @@ Service terminals
 Exercise
 ========
 
-- Ensure you have the DevStack repository cloned to the VM you would like to
-  use it
+- Ensure you have the DevStack repository cloned to the VM where you
+  would like to use it
+- Using the 'screen' command determine if there is a screen session running
+  in your VM.  If there is, attach to it.  If not, start a new session.
+- Once attached to a screen session switch between the running services to
+  get to your favorite service and try stopping and restarting the service.
+- Disconnect from your screen session and ensure it is still running in the
+  background.
+
+.. note::
+
+  - Commands needed:
+
+    - List sessions: screen -ls
+    - Connect: screen -R <session name>
+    - Start a new session:  screen -C devstack/stack-screenrc
+    - Move between services: <ctrl>-a n , <ctrl>-a p
+    - Kill and restart a service: <ctrl>-c , <up arrow> to retrieve command
+    - Disconnect: <ctrl>-a d
+
+