AMQ-5733: return exitcode 0 if stop was sucessful

according to http://refspecs.linuxbase.org/LSB_3.1.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html
the exitcode should be 0, although this is a abnormal termination way

assembly/src/release/bin/activemq

@@ -498,7 +498,7 @@ invoke_stop(){
          echo
          echo "INFO: Regular shutdown not successful,  sending SIGKILL to process with pid '$PID'"
          kill -KILL $PID
-         RET="1"
+         RET="$?"
        fi
     elif [ -f "$ACTIVEMQ_PIDFILE" ];then
        echo "ERROR: No or outdated process id in '$ACTIVEMQ_PIDFILE'"