Due to how clearcase works and our use of the plugin, we use a couple job
variables (NODE_NAME, JOB_NAME) to define the name of the clearcase view. This
value ends up as part of the filesystem. In order to make the build
relocatable, we have to be able to pass these variables to the post build
processors so that they can find all the build output.

This enhancement is to add the build variable processing to the javadoc plugin's
Javadoc directory setting. The code would then need to resolve this directory
at build time with the build parameters.