Add indication of whether a job got killed

We have 'X' for exited with error, add 'K' for killed by
signal as well.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/fio.h b/fio.h
index f59265a..cf2e3c5 100644
--- a/fio.h
+++ b/fio.h
@@ -310,6 +310,7 @@
 		struct frand_state __next_file_state;
 	};
 	int error;
+	int sig;
 	int done;
 	pid_t pid;
 	char *orig_buffer;