attach: wait for exit code from ContainerWait

Such as with `docker run`, if a user CTRL-Cs while attached to a
container, we should forward the signal and wait for the exit from
`ContainerWait`, instead of just returning.

Signed-off-by: Laura Brehm <laurabrehm@hey.com>

cli/command/container/attach_test.go

@@ -1,7 +1,6 @@
 package container
 
 import (
-	"context"
 	"io"
 	"testing"
 
@@ -86,11 +85,7 @@ func TestNewAttachCommandErrors(t *testing.T) {
 }
 
 func TestGetExitStatus(t *testing.T) {
-	var (
-		expectedErr = errors.New("unexpected error")
-		errC        = make(chan error, 1)
-		resultC     = make(chan container.WaitResponse, 1)
-	)
+	expectedErr := errors.New("unexpected error")
 
 	testcases := []struct {
 		result        *container.WaitResponse
@@ -118,20 +113,20 @@ func TestGetExitStatus(t *testing.T) {
 			},
 			expectedError: cli.StatusError{StatusCode: 15},
 		},
-		{
-			err:           context.Canceled,
-			expectedError: nil,
-		},
 	}
 
 	for _, testcase := range testcases {
+		errC := make(chan error, 1)
+		resultC := make(chan container.WaitResponse, 1)
 		if testcase.err != nil {
 			errC <- testcase.err
 		}
 		if testcase.result != nil {
 			resultC <- *testcase.result
 		}
+
 		err := getExitStatus(errC, resultC)
+
 		if testcase.expectedError == nil {
 			assert.NilError(t, err)
 		} else {