docs-rst: Don't go to interactive mode on errors

When building for LaTeX, it stops and enters into interactive
mode on errors. Don't do that, as there are some non-fatal errors
on media books when using Sphinx 1.4.x that we don't know how fix
yet.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>