avoid double counting ec slot

addressing issue found in https://github.com/chrislusf/seaweedfs/issues/1111

The ec slots are already counted on the server side.

weed/shell/command_ec_common.go

@@ -156,7 +156,7 @@ func countShards(ecShardInfos []*master_pb.VolumeEcShardInformationMessage) (cou
 }
 
 func countFreeShardSlots(dn *master_pb.DataNodeInfo) (count int) {
-	return int(dn.FreeVolumeCount)*erasure_coding.DataShardsCount - countShards(dn.EcShardInfos)
+	return int(dn.MaxVolumeCount-dn.ActiveVolumeCount)*erasure_coding.DataShardsCount - countShards(dn.EcShardInfos)
 }
 
 type RackId string
@@ -191,7 +191,8 @@ func collectEcNodes(ctx context.Context, commandEnv *CommandEnv, selectedDataCen
 		if selectedDataCenter != "" && selectedDataCenter != dc {
 			return
 		}
-		if freeEcSlots := countFreeShardSlots(dn); freeEcSlots > 0 {
+
+		freeEcSlots := countFreeShardSlots(dn)
 		ecNodes = append(ecNodes, &EcNode{
 			info:       dn,
 			dc:         dc,
@@ -199,7 +200,6 @@ func collectEcNodes(ctx context.Context, commandEnv *CommandEnv, selectedDataCen
 			freeEcSlot: int(freeEcSlots),
 		})
 		totalFreeEcSlots += freeEcSlots
-		}
 	})
 
 	sortEcNodes(ecNodes)