Simplify the build configuration of the release identifying info

The build currently produces 8 different installations, 2 x 2 x 2, with the factors being full vs servlet, fat vs skinny and legacy build vs galleon. Another factor also is WF vs EAP once the WF code is branched for EAP.

Currently there are some properties and logic related to "product identification" scattered around, which is a pretty unmanageable now. This task is to set the properties in the root pom (where they can easily be updated for later releases or EAP) and then references them elsewhere.

This task is really about a particular subset of things the relate to product.conf and the org.jboss.as.product:<productslot> module. I expect similar things can be done for other strings, but that's not in scope.