Refs #4873 - Add bundle command_execution_module() and adapt command_execution() and its tests

Refs #4873 - Add bundle command_execution_module() and adapt command_execution() and its tests

cf http://www.rudder-project.org/redmine/issues/4873
I suppose that we should use classes based on ${class_prefix} (i.e ${class_prefix}_report_{success,repaired,failed} but it would be difficult to incite users to echo in their scripts something like "command_execution_module__usr_share_local_bin_my_script_sh_report_success".
Is that what you suggest ?