Make NS Consumer message handler thread as joinable thread.

Make NS Consumer message handler thread as joinable thread.

Background:
Currently, NS Consumer message handler thread is a detached thread.
When stopping NS Consumer, we have to destroy thread handle and other resources of message handler thread.
We cannot destroy if message handler thread is running.
So before we destroy, we need to wait for the message handler thread to terminate.
pthread_join() is called internally. As it is on a detached thread, it is useless and it could result in undefined behavior.

https://github.sec.samsung.net/RS7-IOTIVITY/IoTivity/commit/93e66a00acc08ce0c7a3fb217bfb2cc92f2a6c15
(cherry-picked from 93e66a00acc08ce0c7a3fb217bfb2cc92f2a6c15)

Change-Id: I43113a1d6ac0dcbba15a6b12032d71c5369e8b3b
Signed-off-by: Senthil Kumar G S <senthil.gs@samsung.com>
Signed-off-by: Sudipto <sudipto.bal@samsung.com>