Check thread smack label for thread-based app model

Check thread smack label for thread-based app model

Legacy web service app had been launched on a process but
new web service app is launched on a thread to save memory usage.
With the thread-based app model, the thread smack label needs to be checked
from the path |/proc/<tid>/attr/current|.

Also, checking thread smack label is compatible with process-based app model
because main thread utilizes same path of |/proc/<pid>/attr/current| as well.

Change-Id: Ib02237c926a2deedcd91451a36dd2a3d832cfb04
Signed-off-by: Youngsoo Choi <kenshin.choi@samsung.com>