Fix memory leak at thread termination.

Fix memory leak at thread termination.

When push thread done one's works, thread handle does not deallocated.
So, push thread was detached from consumer thread,
and allocated push thread handle was deallocated.

This issue was found on valgrind.

Change-Id: Ia99f960adc8131f2f97f99aa455c19a021abf70f
Signed-off-by: KIM JungYong <jyong2.kim@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/10187
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Madan Lanka <lanka.madan@samsung.com>