create and destroy mission manager in _initialize_this_platform and _reset_this_platform. Creation is particular is now done once there's a platform driver in place to allow mission executive to inspect attributes associated to the driver (eg., commands) in a more generic way. Also, destruction of mission manager consists of aborting all ongoing mission executions.
Merge pull request #2150 from carueda/pa_driver_and_mission_manager

M101: create mission manager when platform driver in place