Do not set wait_for_joins_timeout on 7.x nodes

Author: DaveCTurner

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

@@ -361,7 +361,7 @@ class ClusterFormationTasks {
         if (node.nodeVersion.before("7.0.0") && minimumMasterNodes > 0) {
             esConfig['discovery.zen.minimum_master_nodes'] = minimumMasterNodes
         }
-        if (esConfig.containsKey('discovery.zen.master_election.wait_for_joins_timeout') == false) {
+        if (node.nodeVersion.before("7.0.0") && esConfig.containsKey('discovery.zen.master_election.wait_for_joins_timeout') == false) {
             // If a node decides to become master based on partial information from the pinging, don't let it hang for 30 seconds to correct
             // its mistake. Instead, only wait 5s to do another round of pinging.
             // This is necessary since we use 30s as the default timeout in REST requests waiting for cluster formation