[MSITE-684] mark reportPlugins parameter as read-only, hiding it from generated goal documentation (but not enforcing it won't be used because Maven 3 doesn't check: see MNG-5001)

git-svn-id: https://svn.apache.org/repos/asf/maven/plugins/trunk@1466309 13f79535-47bb-0310-9956-ffa450edef68