allow tests to update the external config registry from properties
diff --git a/core/src/main/java/org/apache/brooklyn/core/mgmt/internal/BasicExternalConfigSupplierRegistry.java b/core/src/main/java/org/apache/brooklyn/core/mgmt/internal/BasicExternalConfigSupplierRegistry.java
index a667ce5..b550813 100644
--- a/core/src/main/java/org/apache/brooklyn/core/mgmt/internal/BasicExternalConfigSupplierRegistry.java
+++ b/core/src/main/java/org/apache/brooklyn/core/mgmt/internal/BasicExternalConfigSupplierRegistry.java
@@ -93,7 +93,7 @@
     }
 
     @SuppressWarnings("unchecked")
-    private void updateFromBrooklynProperties(ManagementContext mgmt) {
+    public void updateFromBrooklynProperties(ManagementContext mgmt) {
         // form is:
         //     brooklyn.external.<name> : fully.qualified.ClassName
         //     brooklyn.external.<name>.<key> : <value>