Check thread smack label for thread-based app model

Check thread smack label for thread-based app model

Web app has been launched on a process but
web service app is launched on a thread and has thread-based app sandboxing
by smack rule. So, 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 web app
because main thread inherits its process smack label from the path
|/proc/self/attr/current|.

Change-Id: I7098ff0672ab4fbb41d1df4e05e435a6cff6e5fc
Signed-off-by: Youngsoo Choi <kenshin.choi@samsung.com>