Renamed ClusterBlocks variable named "block" to "blocks".

"blocks" has been used 9 times for variable names of type
ClusterBlocks but block has been used only this case. It
seems to be a typo.

src/main/java/org/elasticsearch/cluster/ClusterState.java

@@ -497,8 +497,8 @@ public class ClusterState implements ToXContent {
             return blocks(blocksBuilder.build());
         }
 
-        public Builder blocks(ClusterBlocks block) {
-            this.blocks = block;
+        public Builder blocks(ClusterBlocks blocks) {
+            this.blocks = blocks;
             return this;
         }