[Service][Workaround] Make singleton worker thread before app start

[Service][Workaround] Make singleton worker thread before app start

This patch will make singleton webapi worker thread ahead of app
launching to keep it 'User' smack label.
There are lots usage of putting message at singleton worker thread by
 - TaskQueue::GetInstance().Queue()
 - TaskQueue::GetInstance().Async()

tizen.systeminfo.getPropertyValue() is one of API to use TaskQueue
singleton instance.

+ remove unnecessary log

Related patch of filesystem webapi worker issue:
https://review.tizen.org/gerrit/#/c/platform/core/api/webapi-plugins/+/259382/

Change-Id: I7e0abe5e93335d2798bc388f22a88aff754d8d2b
Signed-off-by: DongHyun Song <dh81.song@samsung.com>