fix thread hang issue when send SIGKILL to ktap

There have a long term issue on ktap exit, ktap mainthread
must wait ktapio thread read all content in ring buffer before exit.

Here we use stupid approach to sync with ktapio thread,
note that we cannot use semaphore/completion/other sync method,
because ktapio thread could be killed by SIG_KILL in anytime, there
have no safe way to up semaphore or wake waitqueue before thread exit.

we also cannot use waitqueue of current->signal->wait_chldexit to sync
exit, becasue mainthread and ktapio thread are in same thread group.

Also ktap mainthread must wait ktapio thread exit, otherwise ktapio
thread will oops when access ktap structure.

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>
update test/bench/test.sh

Also remove test/bench/futex.kp, instead use oneline script in
test.sh now.

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>
use kp_error for error report as possible

Signed-off-by: zhangwei(Jovi) <jovi.zhangwei@gmail.com>