Consolidate disk util, eta, and status check thread

We don't need two, we can just have one do everything.

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/fio.h b/fio.h
index f981739..f453d92 100644
--- a/fio.h
+++ b/fio.h
@@ -403,6 +403,8 @@
 extern int log_syslog;
 extern int status_interval;
 extern const char fio_version_string[];
+extern int helper_do_stat;
+extern pthread_cond_t helper_cond;
 
 extern struct thread_data *threads;