ease configuration of the metadata storage factory

git-svn-id: https://svn.apache.org/repos/asf/archiva/trunk@1582569 13f79535-47bb-0310-9956-ffa450edef68
fix @since

git-svn-id: https://svn.apache.org/repos/asf/archiva/trunk@1582570 13f79535-47bb-0310-9956-ffa450edef68