fn: I/O related improvements (#809)

*) I/O protocol parse issues should shutdown the container as the container
goes to inconsistent state between calls. (eg. next call may receive previous
calls left overs.)
*) Move ghost read/write code into io_utils in common.
*) Clean unused error from docker Wait()
*) We can catch one case in JSON, if there's remaining unparsed data in
decoder buffer, we can shut the container
*) stdout/stderr when container is not handling a request are now blocked if freezer is also enabled.
*) if a fatal err is set for slot, we do not requeue it and proceed to shutdown
*) added a test function for a few cases with freezer strict behavior

api/agent/drivers/docker/docker.go

@@ -384,7 +384,7 @@ type waitResult struct {
 }
 
 // waitResult implements drivers.WaitResult
-func (w *waitResult) Wait(ctx context.Context) (drivers.RunResult, error) {
+func (w *waitResult) Wait(ctx context.Context) drivers.RunResult {
 	defer close(w.done)
 
 	// wait until container is stopped (or ctx is cancelled if sooner)
@@ -392,7 +392,7 @@ func (w *waitResult) Wait(ctx context.Context) (drivers.RunResult, error) {
 	return &runResult{
 		status: status,
 		err:    err,
-	}, nil
+	}
 }
 
 // Repeatedly collect stats from the specified docker container until the stopSignal is closed or the context is cancelled

api/agent/drivers/docker/docker_test.go

@@ -56,9 +56,9 @@ func TestRunnerDocker(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	result, err := waiter.Wait(ctx)
-	if err != nil {
-		t.Fatal(err)
+	result := waiter.Wait(ctx)
+	if result.Error() != nil {
+		t.Fatal(result.Error())
 	}
 
 	if result.Status() != "success" {
@@ -109,9 +109,9 @@ func TestRunnerDockerStdin(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	result, err := waiter.Wait(ctx)
-	if err != nil {
-		t.Fatal(err)
+	result := waiter.Wait(ctx)
+	if result.Error() != nil {
+		t.Fatal(result.Error())
 	}
 
 	if result.Status() != "success" {