When we are about to finish waiting, report that instead of unknown

core/src/main/java/hudson/model/Queue.java

@@ -2490,7 +2490,7 @@ public class Queue extends ResourceController implements Saveable {
             if (diff >= 0)
                 return CauseOfBlockage.fromMessage(Messages._Queue_InQuietPeriod(Util.getTimeSpanString(diff)));
             else
-                return CauseOfBlockage.fromMessage(Messages._Queue_Unknown());
+                return CauseOfBlockage.fromMessage(Messages._Queue_FinishedWaiting());
         }
 
         @Override

core/src/main/resources/hudson/model/Messages.properties

@@ -200,6 +200,7 @@ Queue.InProgress=A build is already in progress
 Queue.InQuietPeriod=In the quiet period. Expires in {0}
 Queue.NodeOffline=\u2018{0}\u2019 is offline
 Queue.Unknown=???
+Queue.FinishedWaiting=Finished waiting
 Queue.WaitingForNextAvailableExecutor=Waiting for next available executor
 Queue.WaitingForNextAvailableExecutorOn=Waiting for next available executor on \u2018{0}\u2019
 Queue.init=Restoring the build queue