Use Sphinx 1.5 warning-is-error

With pbr 2.0 and Sphinx 1.5, the setting for treat sphinx warnings as
errors is setting warning-is-error in build_sphinx section. Migrate the
setting from the old warnerrors one.

There are only three related fixes required.

Change-Id: I84b020c18a8a1c7c11a35bacd61523bbb094abe4

doc/source/shell.rst

@@ -10,10 +10,10 @@ from the command line. It supports the entirety of the OpenStack Nova API.
 First, you'll need an OpenStack Nova account and an API key. You get this
 by using the `nova-manage` command in OpenStack Nova.
 
-You'll need to provide :program:`nova` with your OpenStack username and
-API key. You can do this with the :option:`--os-username`, :option:`--os-password`
-and :option:`--os-tenant-id` options, but it's easier to just set them as
-environment variables by setting two environment variables:
+You'll need to provide :program:`nova` with your OpenStack username and API
+key. You can do this with the `--os-username`, `--os-password` and
+`--os-tenant-id` options, but it's easier to just set them as environment
+variables by setting two environment variables:
 
 .. envvar:: OS_USERNAME
 
@@ -42,9 +42,9 @@ For example, in Bash you'd use::
     export OS_TENANT_NAME=myproject
     export OS_AUTH_URL=http://...
     export OS_COMPUTE_API_VERSION=2
-    
+
 From there, all shell commands take the form::
-    
+
     nova <command> [arguments...]
 
 Run :program:`nova help` to get a full list of all possible commands,

setup.cfg

@@ -31,9 +31,10 @@ console_scripts =
     nova = novaclient.shell:main
 
 [build_sphinx]
+all-files = 1
+warning-is-error = 1
 source-dir = doc/source
 build-dir = doc/build
-all_files = 1
 
 [upload_sphinx]
 upload-dir = doc/build/html
@@ -54,6 +55,3 @@ output_file = novaclient/locale/novaclient.pot
 
 [wheel]
 universal = 1
-
-[pbr]
-warnerrors = true