Avoid serialising state if it was already serialised (elastic#39179)

When preparing the state to send to other nodes, we're serializing it
for each node, despite using putIfAbsent.
This commit checks if the state was already serialized for this node
version before performing the potentially expensive computation.
The map is not used by multiple threads, so computeIfAbsent is not
needed (and could not be used here easily, because IOException could
be thrown).

(cherry picked from commit c99be63)

Author: Andrey Ershov

server/src/main/java/org/elasticsearch/cluster/coordination/PublicationTransportHandler.java

@@ -320,13 +320,17 @@ private static void buildDiffAndSerializeStates(ClusterState clusterState, Clust
             }
             try {
                 if (sendFullVersion || !previousState.nodes().nodeExists(node)) {
-                    serializedStates.putIfAbsent(node.getVersion(), serializeFullClusterState(clusterState, node.getVersion()));
+                    if (serializedStates.containsKey(node.getVersion()) == false) {
+                        serializedStates.put(node.getVersion(), serializeFullClusterState(clusterState, node.getVersion()));
+                    }
                 } else {
                     // will send a diff
                     if (diff == null) {
                         diff = clusterState.diff(previousState);
                     }
-                    serializedDiffs.putIfAbsent(node.getVersion(), serializeDiffClusterState(diff, node.getVersion()));
+                    if (serializedDiffs.containsKey(node.getVersion()) == false) {
+                        serializedDiffs.put(node.getVersion(), serializeDiffClusterState(diff, node.getVersion()));
+                    }
                 }
             } catch (IOException e) {
                 throw new ElasticsearchException("failed to serialize cluster state for publishing to node {}", e, node);