Add support for specifying UID/GID

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/fio.h b/fio.h
index b1af7b1..3b2dd6e 100644
--- a/fio.h
+++ b/fio.h
@@ -277,6 +277,9 @@
 	 */
 	char *cgroup;
 	unsigned int cgroup_weight;
+
+	unsigned int uid;
+	unsigned int gid;
 };
 
 #define FIO_VERROR_SIZE	128