Revert unwanted commits accidentally included from master

Commit 3e019c2 was accidentally based on a commit on the master
branch, and caused a couple of commits from master to be included
in stable-2.8:

- "Update VERSION file to 2.9-SNAPSHOT"
- "Update version to 2.9-SNAPSHOT in plugin archetype pom files"

This reverts commit 8914d9ddf0acda15df3861dcc2a0ca10bd94ceca.
This reverts commit 62864b7a8a9e2ce7828234c1de181342ccfdde8b.

Change-Id: Idfd195061228274557035a0a6035bbd656ec693c