Standardize command usage messages with cmd_usage()

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
diff --git a/common/cmd_itest.c b/common/cmd_itest.c
index 9e77fa9..b3025e3 100644
--- a/common/cmd_itest.c
+++ b/common/cmd_itest.c
@@ -161,7 +161,7 @@
 
 	/* Validate arguments */
 	if ((argc != 4)){
-		printf("Usage:\n%s\n", cmdtp->usage);
+		cmd_usage(cmdtp);
 		return 1;
 	}