[SPARK-3597][Mesos] Implement `killTask`.

The MesosSchedulerBackend did not previously implement `killTask`,
resulting in an exception.

Author: Brenden Matthews <brenden@diddyinc.com>

Closes #2453 from brndnmtthws/implement-killtask and squashes the following commits:

23ddcdc [Brenden Matthews] [SPARK-3597][Mesos] Implement `killTask`.

(cherry picked from commit 32fad423)
Signed-off-by: Andrew Or <andrewor14@gmail.com>

core/src/main/scala/org/apache/spark/scheduler/cluster/mesos/MesosSchedulerBackend.scala

@@ -369,6 +369,13 @@ private[spark] class MesosSchedulerBackend(
     recordSlaveLost(d, slaveId, ExecutorExited(status))
   }
 
+  override def killTask(taskId: Long, executorId: String, interruptThread: Boolean): Unit = {
+    driver.killTask(
+      TaskID.newBuilder()
+        .setValue(taskId.toString).build()
+    )
+  }
+
   // TODO: query Mesos for number of cores
   override def defaultParallelism() = sc.conf.getInt("spark.default.parallelism", 8)
 }