Add getSlaves() to approved Jenkins methods

Change-Id: I9e548d32b5be0a655cd0e38efce7689dc4ea1786
diff --git a/jenkins/client/approved_scripts.yml b/jenkins/client/approved_scripts.yml
index 7d470b6..8586e49 100644
--- a/jenkins/client/approved_scripts.yml
+++ b/jenkins/client/approved_scripts.yml
@@ -17,6 +17,7 @@
         - method groovy.util.XmlParser parseText java.lang.String
         - method hudson.PluginManager getPlugins
         - method hudson.PluginWrapper getShortName
+        - method hudson.model.Hudson getSlaves
         - method hudson.model.Item getName
         - method hudson.model.ItemGroup getItem java.lang.String
         - method hudson.model.ItemGroup getItems