[DOC FIX] Create missing index pages

There was a mistake in the documentation migration.  The
landing pages in the admin and configuration sections should
have been moved to index.html.  That step didn't happen which
is causing it to appear that that content is missing from
the main OpenStack docs website.

This patch updates our main index page and moves the existing
landing pages to index.rst.

Change-Id: Idb96a09f748d3bbebf6eb768dfd2b758da545096

doc/source/index.rst

@@ -55,7 +55,7 @@ Cinder installation.
 .. toctree::
    :maxdepth: 2
 
-   admin/blockstorage
+   admin/index
 
 Contributor/Developer Docs
 ~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -116,7 +116,7 @@ available for Cinder including a sample configuration file.
 .. toctree::
     :maxdepth: 1
 
-    configuration/block-storage
+    configuration/index
     sample_config
 
 Indices and tables