bug fix: twist cmd for semi emergency stop plan

Fixed bug

As semi-emergency stop plan only sends emergency control command and not twist_cmd, unexpected behavior will be observed with vehicles using twist_cmd for their control.

Required information:

• Operating system and version: Ubuntu 16.04
• Autoware installation type: From source
• Autoware version or commit hash: Common:d0fd0c48
• ROS distribution and version: Kinetic
• ROS installation type:From source
• Package or library, if applicable: emergency_handler

Description of the bug

semi-emergency stop plan does not work correctly when IDEAL_TWIST is chosen as "vehicle_model_type Source" for wf_simulator

Steps to reproduce the bug

1. Launch roscore and runtime manager
2. Launch autoware_health_aggregator
3. Launch emergency handler with the following parameters

emergency_spdctl_max_dec: 1.0
emergency_planner_enabled: true
emergency_planner:
  emergency_stop_planner: 0
  semi-emergency_stop_planner: 1
emergency_handling_priority:
  node_error: 1
  hardware_error: 0
  emergency_handler_error: 0
vital_monitor:
  decision_maker:
    timeout: 0.1
    level: 4

1. Launch decision maker
2. Launch rviz
3. Launch necessary nodes to start wf simulator
4. Choose IDEAL_TWIST as "vehicle_model_type Source" for wf_simulator
5. Launch wf simulator
6. Confirm vehicle is moving along waypoints
7. Kill decision maker
8. Confirm semi-emergency stop does not work properly and the vehicle does not stop.

Expected behavior

The vehicle is gradually stop(dec rate is 1.0[m/s]) in wf simulator

Actual behavior

The vehicle does not stop in wf simulator