Fix relocating shards size calculation (#48421)

In #48392 we added a second computation of the sizes of the relocating shards
in `canRemain()` but passed the wrong value for `subtractLeavingShards`. This
fixes that. It also removes some unnecessary logging in a test case added in
the same commit.

Author: DaveCTurner

server/src/main/java/org/elasticsearch/cluster/routing/allocation/decider/DiskThresholdDecider.java

@@ -317,7 +317,7 @@ public Decision canRemain(ShardRouting shardRouting, RoutingNode node, RoutingAl
                     "this shard is not allocated on the most utilized disk and can remain");
         }
         if (freeBytes < 0L) {
-            final long sizeOfRelocatingShards = sizeOfRelocatingShards(node, false, usage.getPath(),
+            final long sizeOfRelocatingShards = sizeOfRelocatingShards(node, true, usage.getPath(),
                 allocation.clusterInfo(), allocation.metaData(), allocation.routingTable());
             logger.debug("fewer free bytes remaining than the size of all incoming shards: " +
                     "usage {} on node {} including {} bytes of relocations, shard cannot remain",

server/src/test/java/org/elasticsearch/cluster/routing/allocation/decider/DiskThresholdDeciderTests.java

@@ -754,17 +754,13 @@ public void testShardRelocationsTakenIntoAccount() {
             AllocationCommand moveAllocationCommand = new MoveAllocationCommand("test2", 0, "node2", "node3");
             AllocationCommands cmds = new AllocationCommands(moveAllocationCommand);
 
-            logger.info("--> before starting: {}", clusterState);
             clusterState = startInitializingShardsAndReroute(strategy, clusterState);
-            logger.info("--> after starting: {}", clusterState);
             clusterState = strategy.reroute(clusterState, cmds, false, false).getClusterState();
-            logger.info("--> after running another command: {}", clusterState);
             logShardStates(clusterState);
 
             clusterInfoReference.set(overfullClusterInfo);
 
-            clusterState = strategy.reroute(clusterState, "foo");
-            logger.info("--> after another reroute: {}", clusterState);
+            strategy.reroute(clusterState, "foo"); // ensure reroute doesn't fail even though there is negative free space
         }
     }