Add log_info_flush()

If fio dumps status through -USR1 or similar and output is
being stored in a file, the buffering on the file descriptor
by the library can cause is not to see all the output. Ensure
that it gets flushed after dumping stats.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/log.c b/log.c
index d481edf..4822c33 100644
--- a/log.c
+++ b/log.c
@@ -71,6 +71,14 @@
 		return fwrite(buffer, len, 1, f_out);
 }
 
+int log_info_flush(void)
+{
+	if (is_backend || log_syslog)
+		return 0;
+
+	return fflush(f_out);
+}
+
 int log_err(const char *format, ...)
 {
 	char buffer[1024];