wait until the thread is stopped.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47667 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
(test_main_thread_status_at_exit) wait until the thread enter the begin clause. 


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@47668 b2dd03c8-39d4-4d8f-98ff-823fe69b080e