Add the integ test node's configuration directory as a system property

buildSrc/src/main/groovy/org/elasticsearch/gradle/test/RestIntegTestTask.groovy

@@ -62,6 +62,7 @@ public class RestIntegTestTask extends RandomizedTestingTask {
         project.gradle.projectsEvaluated {
             NodeInfo node = ClusterFormationTasks.setup(project, this, clusterConfig)
             systemProperty('tests.rest.cluster', "${-> node.httpUri()}")
+            systemProperty('tests.config.dir', "${-> node.confDir}")
             // TODO: our "client" qa tests currently use the rest-test plugin. instead they should have their own plugin
             // that sets up the test cluster and passes this transport uri instead of http uri. Until then, we pass
             // both as separate sysprops