client: emit event and call exited hooks during cleanup

Builds upon earlier commit that cleans up restored handles of terminal
allocs by also emitting terminated events and calling exited hooks when
appropriate.

client/allocrunner/taskrunner/task_runner.go

@@ -493,7 +493,15 @@ MAIN:
 	// that should be terminal, so if the handle still exists we should
 	// kill it here.
 	if tr.getDriverHandle() != nil {
-		tr.handleKill()
+		if result = tr.handleKill(); result != nil {
+			tr.emitExitResultEvent(result)
+		}
+
+		tr.clearDriverHandle()
+
+		if err := tr.exited(); err != nil {
+			tr.logger.Error("exited hooks failed while cleaning up terminal task", "error", err)
+		}
 	}
 
 	// Mark the task as dead
@@ -540,6 +548,14 @@ func (tr *TaskRunner) handleTaskExitResult(result *drivers.ExitResult) (retryWai
 		return true
 	}
 
+	// Emit Terminated event
+	tr.emitExitResultEvent(result)
+
+	return false
+}
+
+// emitExitResultEvent emits a TaskTerminated event for an ExitResult.
+func (tr *TaskRunner) emitExitResultEvent(result *drivers.ExitResult) {
 	event := structs.NewTaskEvent(structs.TaskTerminated).
 		SetExitCode(result.ExitCode).
 		SetSignal(result.Signal).
@@ -551,8 +567,6 @@ func (tr *TaskRunner) handleTaskExitResult(result *drivers.ExitResult) (retryWai
 	if result.OOMKilled && !tr.clientConfig.DisableTaggedMetrics {
 		metrics.IncrCounterWithLabels([]string{"client", "allocs", "oom_killed"}, 1, tr.baseLabels)
 	}
-
-	return false
 }
 
 // handleUpdates runs update hooks when triggerUpdateCh is ticked and exits