Fix timing issue

Fix timing issue

Following scenario can occur. (Th: thread)
1. Th1: Call vine_dp_open()
2. Th2: opened_cb isn't invoked yet.
3. Th1: Call vine_dp_close() or vine_dp_destroy()
4. Th2: Access to freed memory

LWS with external poll doesn't provide API for cancel websocket creation.
So, This patch handles close() and destroy() request in internal thread(Th2).

Change-Id: I394786fdfb5b7cf161ef4d2a904b9ba5d9960b2d