Change PDF file name

The previously choosen PDF file name conflicts in some repos with the
project logos (badge). Thus change https://review.opendev.org/679777
renames the desired PDF name to be doc-PROJECT.pdf to allow using the
badge in PDF files.

Follow this rename.

Change-Id: I6fbddc841039a9a66998b4ca7ae81742852d12ae

doc/source/conf.py

@@ -61,7 +61,7 @@ bug_tag = ''
 # (source start file, target name, title, author, documentclass
 # [howto/manual]).
 latex_documents = [
-    ('index', 'os-brick.tex', u'OS Brick Documentation',
+    ('index', 'doc-os-brick.tex', u'OS Brick Documentation',
      'Cinder Contributors', 'manual')
 ]