Fix dist and servlet-dist module to use jboss.as.release.version

https://developer.jboss.org/thread/224262 announced availability of WildFly nightly builds.

Current status is that you must know the URL based on current version in master
At this moment it is https://ci.wildfly.org/guestAuth/repository/download/WF_Nightly/latest.lastFinished/wildfly-11.0.0.Final-SNAPSHOT.zip, root dir of the zip is wildfly-11.0.0.Final-SNAPSHOT

'11.0.0.Final-SNAPSHOT' is the changing part and when you want to consume nightly build in CI (e.g. Travis) you end up doing unnecessary changes to .travis.yml (Alpha1-SNAPSHOT ==> Beta1-SNAPSHOT ==> Final-SNAPSHOT) when PRs fail because of unavailable nightly bits

Proposal 1 - expose latest bits under the same URL + keep the same root dir name
URL: https://ci.wildfly.org/guestAuth/repository/download/WF_Nightly/latest.lastFinished/wildfly-latest-SNAPSHOT.zip
root dir of the zip: wildfly-latest-SNAPSHOT

Automation would be prepared just once and "work forever".

Usage of project.version in dist and servlet-dist module prevents to use mvn clean install -Djboss.as.release.version=latest-SNAPSHOT to adjust final zip & root dir name.

Discussion starting point: http://lists.jboss.org/pipermail/wildfly-dev/2017-September/006052.html