The short answer is that I resolved the associated JIRA (JBTM-1470) as follows:

"This feature is no longer required so I will resolve it by removing the option to conditionally build the AS (ie I will remove the env variable AS_BUILD)". 

The longer answer is that previously not building the AS meant that the artifacts from the narayana build were copied over to the AS modules directory to make sure the AS was running with the latest changes. So each time we produce a new AS deployable artifact or change the name of an existing one the person making the change needed to remember to update the narayana.sh script as well and this was error prone - since the CI runs always build the AS I took the view that we were better off removing the option.

But if anyone finds the feature useful I will be happy to reinstate it. Do you find it useful?