Revert "Revert "poky: subtree update:b23aa6b753..ad30a6d470""

This reverts commit 4873add6e11c1bd421c83cd08df589f1184aa673.

A fix has been put up for openbmc/openbmc#3720 so we can bring
this back now

Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: If59020a5b502f70aa7149fbef4ad2f50824d1ce6
diff --git a/poky/bitbake/doc/conf.py b/poky/bitbake/doc/conf.py
index 197f275..354dff3 100644
--- a/poky/bitbake/doc/conf.py
+++ b/poky/bitbake/doc/conf.py
@@ -73,7 +73,13 @@
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.
 #
-html_theme = 'sphinx_rtd_theme'
+try:
+    import sphinx_rtd_theme
+    html_theme = 'sphinx_rtd_theme'
+except ImportError:
+    sys.stderr.write("The Sphinx sphinx_rtd_theme HTML theme was not found.\
+    \nPlease make sure to install the sphinx_rtd_theme python package.\n")
+    sys.exit(1)
 
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,