Only use boost workers for leveldb shadow queues (#15696)

* The leveldb shadow queue of a persistable channel queue should always start with 0
workers and just use boost to add additional workers if necessary.

* create a zero boost so that if there are no workers in a pool - boost to start the workers

* actually set timeout appropriately on boosted workers

Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/queue/queue_disk_channel.go

@@ -75,10 +75,10 @@ func NewPersistableChannelQueue(handle HandlerFunc, cfg, exemplar interface{}) (
 				BatchLength:  config.BatchLength,
 				BlockTimeout: 1 * time.Second,
 				BoostTimeout: 5 * time.Minute,
-				BoostWorkers: 5,
-				MaxWorkers:   6,
+				BoostWorkers: 1,
+				MaxWorkers:   5,
 			},
-			Workers: 1,
+			Workers: 0,
 			Name:    config.Name + "-level",
 		},
 		DataDir: config.DataDir,