Actually interpolate log string

Author: srowen

core/src/main/scala/org/apache/spark/scheduler/cluster/CoarseGrainedSchedulerBackend.scala

@@ -103,7 +103,7 @@ class CoarseGrainedSchedulerBackend(scheduler: TaskSchedulerImpl, val rpcEnv: Rp
             case None =>
               // Ignoring the update since we don't know about the executor.
               logWarning(s"Ignored task status update ($taskId state $state) " +
-                "from unknown executor with ID $executorId")
+                s"from unknown executor with ID $executorId")
           }
         }