Revise shutdown command function

Revise shutdown command function

- Previously, camera_stop_preview() and camera_destroy() in shutdown command function could be failed
  when camera_stop_preview() is already executing in task thread by client's request at the same time.
- This patch adds new job to stop preview for shutdown command
  and it prevents to execute camera_stop_preview() in shutdown command and task thread concurrently.

[Version] 0.3.60
[Issue Type] Improvement

Change-Id: I851821788a2c8a8c3c83d6f8155833a4f234b1ef
Signed-off-by: Jeongmo Yang <jm80.yang@samsung.com>