Use the oslo.config sphinx module to generate sample

This commit switches to using the oslo.config sphinx extension to
generate a sample config instead of doing it manually in the docs'
conf.py module.

Change-Id: I7032cb4f56c728911ffa5c6911eb504f53bc80af
diff --git a/doc/source/conf.py b/doc/source/conf.py
index 3ec25ea..f85899b 100644
--- a/doc/source/conf.py
+++ b/doc/source/conf.py
@@ -15,18 +15,6 @@
 import os
 import subprocess
 
-# Build a tempest sample config file:
-def build_sample_config(app):
-    root_dir = os.path.dirname(
-        os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
-    subprocess.call(["oslo-config-generator", "--config-file",
-                     "tools/config/config-generator.tempest.conf",
-                     "--output-file", "doc/source/_static/tempest.conf"],
-                    cwd=root_dir)
-
-def setup(app):
-    app.connect('builder-inited', build_sample_config)
-
 # If extensions (or modules to document with autodoc) are in another directory,
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
@@ -42,9 +30,13 @@
 extensions = ['sphinx.ext.autodoc',
               'sphinx.ext.todo',
               'sphinx.ext.viewcode',
-              'oslosphinx'
+              'oslosphinx',
+              'oslo_config.sphinxconfiggen',
              ]
 
+config_generator_config_file = '../../tools/config/config-generator.tempest.conf'
+sample_config_basename = '_static/tempest'
+
 todo_include_todos = True
 
 # Add any paths that contain templates here, relative to this directory.