Add missing cors settings for glance.control.single

We've switched to direct upload mode in horizon, which is requiring
cors to be enabled on glance sinde. This patch adds missed
part to glance.control.single

Change-Id: I5178f32c6191dcab6dd8df626f461068e3e61fc7
Related-Prod: PROD-25937
diff --git a/glance/control/single.yml b/glance/control/single.yml
index 694c395..ee2ae1a 100644
--- a/glance/control/single.yml
+++ b/glance/control/single.yml
@@ -48,3 +48,5 @@
           enabled: ${_param:glance_memcache_security_enabled}
           strategy: ${_param:openstack_memcache_security_strategy}
           secret_key: ${_param:glance_memcache_secret_key}
+      cors:
+        allowed_origin: ${_param:glance_cors_allowed_origin}