Architecture html docs are missing diagrams

[cppwfs]

The diagrams in the html (index.html) are not displayed. However they do show up in the html-single (index-single.hmtl) and PDF docs.

[cppwfs]

This is caused by the batch-asciidoc variable not being set for the spring-batch-architecture.adoc when it is used without being included by the html-single.adoc.