Fix building of translated Install Guides on Mitaka

This fixes https://review.openstack.org/#/c/427596 - to skip the Debconf
guide if it does not exist.

Change-Id: Ic78068b9ce08f878049a07e1bb7891ccf4aa58ab

bin/doc-tools-check-languages

@@ -242,8 +242,11 @@ function handle_draft_language {
                 ;;
             install-guide)
                 for tag in $INSTALL_TAGS ; do
-                    mv publish-docs/$language/$book-${tag} \
-                        publish-docs/draft/$language/$book-${tag}
+                    # Not all tags might be build on all branches
+                    if [[ -d publish-docs/$language/$book-${tag} ]] ; then
+                        mv publish-docs/$language/$book-${tag} \
+                            publish-docs/draft/$language/$book-${tag}
+                    fi
                 done
                 rmdir --ignore-fail-on-non-empty publish-docs/$language/
                 ;;

releasenotes/notes/docbuild-mitaka-52668f8862e88552.yaml

@@ -0,0 +1,4 @@
+---
+fixes:
+  - Fix building of translations on older branches where the DebConf
+    Install Guide does not exist.