Add PDF documentation build

This commit adds PDF documentation build target 'pdf-docs' that will
build PDF versions of our docs. As per the Train community goal:

 https://governance.openstack.org/tc/goals/selected/train/pdf-doc-generation.html

Change-Id: Iecb0fe5b957af7dae66bea04dfbd9c2fb4f74a99
Story: #2006070
Task: #35456

doc/source/conf.py

@@ -165,7 +165,7 @@ htmlhelp_basename = 'DevStack-doc'
 # Grouping the document tree into LaTeX files. List of tuples
 # (source start file, target name, title, author, documentclass [howto/manual]).
 latex_documents = [
-  ('index', 'DevStack-doc.tex', u'DevStack Docs',
+  ('index', 'doc-devstack.tex', u'DevStack Docs',
    u'OpenStack DevStack Team', 'manual'),
 ]
 

doc/source/index.rst

@@ -11,9 +11,8 @@
    and how to go beyond this setup. Both should be a set of quick
    links to other documents to let people explore from there.
 
-==========
 DevStack
-==========
+========
 
 .. image:: assets/images/logo-blue.png
 
@@ -32,7 +31,7 @@ The source is available at `<https://opendev.org/openstack/devstack>`__.
    are dedicated to this purpose.
 
 Quick Start
-===========
++++++++++++
 
 Install Linux
 -------------
@@ -153,7 +152,7 @@ with devstack, and help us by :doc:`contributing to the project
 <hacking>`.
 
 Contents
---------
+++++++++
 
 .. toctree::
    :glob:

tox.ini

@@ -43,6 +43,14 @@ setenv =
 commands =
   sphinx-build -W -b html -d doc/build/doctrees doc/source doc/build/html
 
+[testenv:pdf-docs]
+basepython = python3
+deps = {[testenv:docs]deps}
+whitelist_externals =
+   make
+commands =
+   sphinx-build -W -b latex doc/source doc/build/pdf
+   make -C doc/build/pdf
 
 [testenv:venv]
 basepython = python3