Upgrade Maven Plugin plugin to version 2.9

Release Notes - Maven 2.x Plugin Tools - Version 2.9

** Bug
    * [MPLUGIN-177] - Required JDK incorrectly specified if using default for m-compiler-p
    * [MPLUGIN-186] - Plugins with no mojos lead to exception and failure in PluginReport

** Improvement
    * [MPLUGIN-124] - The generated documentation for a Mojo should show if it is a build plugin or a reporting plugin
    * [MPLUGIN-179] - Clarify the goalPrefix (is there a default value for example) param

** Task
    * [MPLUGIN-120] - Update to Doxia 1.2