fix failing thread object run

A previously exited Thread object refuses to run again, if the
thread-id of the caller, conincides with the thread-id it previously
used in the worker thread. Hence reset the previously used worker
thread-id to -1 when it exits.

Signed-off-by: Ritu Srivastava <rsrivast@sta.samsung.com>

Change-Id: I873925c312a43ec8a16392b98cc959042ff6bfd2

Signed-off-by: Madan Ankapura <mankapur@sta.samsung.com>