Internal: Flatten ClusterModule and add more tests

The ClusterModule contained a couple submodules. This moves the
functionality from those modules into ClusterModule. Two of those
had to do with DynamicSettings. This change also cleans up
how DynamicSettings are built, and enforces they are added, with
validators, in ClusterModule.

See elastic#12783.

core/src/main/java/org/elasticsearch/action/admin/cluster/settings/TransportClusterUpdateSettingsAction.java

@@ -183,7 +183,7 @@ public ClusterState execute(final ClusterState currentState) {
                 transientSettings.put(currentState.metaData().transientSettings());
                 for (Map.Entry<String, String> entry : request.transientSettings().getAsMap().entrySet()) {
                     if (dynamicSettings.isDynamicOrLoggingSetting(entry.getKey())) {
-                        String error = dynamicSettings.validateDynamicSetting(entry.getKey(), entry.getValue());
+                        String error = dynamicSettings.validateDynamicSetting(entry.getKey(), entry.getValue(), clusterService.state());
                         if (error == null) {
                             transientSettings.put(entry.getKey(), entry.getValue());
                             transientUpdates.put(entry.getKey(), entry.getValue());
@@ -200,7 +200,7 @@ public ClusterState execute(final ClusterState currentState) {
                 persistentSettings.put(currentState.metaData().persistentSettings());
                 for (Map.Entry<String, String> entry : request.persistentSettings().getAsMap().entrySet()) {
                     if (dynamicSettings.isDynamicOrLoggingSetting(entry.getKey())) {
-                        String error = dynamicSettings.validateDynamicSetting(entry.getKey(), entry.getValue());
+                        String error = dynamicSettings.validateDynamicSetting(entry.getKey(), entry.getValue(), clusterService.state());
                         if (error == null) {
                             persistentSettings.put(entry.getKey(), entry.getValue());
                             persistentUpdates.put(entry.getKey(), entry.getValue());

core/src/main/java/org/elasticsearch/cluster/metadata/MetaDataUpdateSettingsService.java

@@ -191,7 +191,7 @@ public void updateSettings(final UpdateSettingsClusterStateUpdateRequest request
             if (!dynamicSettings.hasDynamicSetting(setting.getKey())) {
                 removedSettings.add(setting.getKey());
             } else {
-                String error = dynamicSettings.validateDynamicSetting(setting.getKey(), setting.getValue());
+                String error = dynamicSettings.validateDynamicSetting(setting.getKey(), setting.getValue(), clusterService.state());
                 if (error != null) {
                     errors.add("[" + setting.getKey() + "] - " + error);
                 }

core/src/main/java/org/elasticsearch/cluster/routing/allocation/decider/ClusterRebalanceAllocationDecider.java

@@ -19,6 +19,7 @@
 
 package org.elasticsearch.cluster.routing.allocation.decider;
 
+import org.elasticsearch.cluster.ClusterState;
 import org.elasticsearch.cluster.routing.ShardRouting;
 import org.elasticsearch.cluster.routing.allocation.RoutingAllocation;
 import org.elasticsearch.cluster.settings.Validator;
@@ -52,7 +53,7 @@ public class ClusterRebalanceAllocationDecider extends AllocationDecider {
     public static final String CLUSTER_ROUTING_ALLOCATION_ALLOW_REBALANCE = "cluster.routing.allocation.allow_rebalance";
     public static final Validator ALLOCATION_ALLOW_REBALANCE_VALIDATOR = new Validator() {
         @Override
-        public String validate(String setting, String value) {
+        public String validate(String setting, String value, ClusterState clusterState) {
             try {
                 ClusterRebalanceType.parseString(value);
                 return null;