[thread] Fix the comment of Thread
[thread] Fix the comment of Thread

In the current implementation(i.e. from commit 9fa9cf181d),
the handshake is no longer needed between the parent thread
and the child thread, but the comments are not updated
in time, which can lead to misunderstanding

Change-Id: Ib493fa0e33bb55cf436d7894cc87854337919854
Reviewed-on: http://gerrit.cloudera.org:8080/14308
Tested-by: Kudu Jenkins
Reviewed-by: Adar Dembo <866ca730bfc7f544e3ebce604ceeba4879f23df0@cloudera.com>

helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu,helifu/kudu