Fix heat role create error

https://review.openstack.org/#/c/76036/ changed the user creat commands,
missed the argument to --user

Change-Id: Iaf10ef80a2fb0227dd66a314e7ec253dfb4dc4fe
diff --git a/lib/heat b/lib/heat
index 1b6dc86..972c35c 100644
--- a/lib/heat
+++ b/lib/heat
@@ -214,7 +214,7 @@
         --description "Manages users and projects created by heat"
     openstack --os-token $OS_TOKEN --os-url=$KS_ENDPOINT_V3 \
         --os-identity-api-version=3 role add \
-        --user ${U_ID} --domain ${D_ID} admin
+        --user heat_domain_admin --domain ${D_ID} admin
     iniset $HEAT_CONF DEFAULT stack_domain_admin heat_domain_admin
     iniset $HEAT_CONF DEFAULT stack_domain_admin_password $SERVICE_PASSWORD
 }