Automatic versioning in invoker tests

This avoids manual version bumping in the tests after a new version of the project has been released (like commit 5d87cce4b67e9d0a9ed36f70ff54b09e3a2484b7)

This pull request uses the maven-invoker-plugin [filtering](http://maven.apache.org/plugins/maven-invoker-plugin/examples/filtering.html) feature to perform that.
In addition, groupId and artifactId are now also filtered.