Install maven after Java is installed.

* modules/jenkins/manifests/slave.pp: Ensure that maven is installed
after we install Java so that we can control the version of Java that is
installed. Without this maven will pull in whichever version of Java it
has in its dependency list.

Change-Id: I36b27ea654c31c71aaca2d4a8f93e0557c7b4930
Merge "Install maven after Java is installed."