rtt_rosclock: added cleanup function to terminate SimClockThread when the application quits

If the SimClockThread is not destroyed by the StartStopManager before the Logger is finally destroyed in __os_exit(),
RTT will restart the Logger due to log output in the RTT::os::Thread::~Thread() destructor and overwrite the orocos.log file.
Merge branch 'hydro-devel' into rtt_dynamic_reconfigure