Update TestContext_sleepTimeoutExpired to check for canceling within timeframe

Add a timeout to the test to ensure that the terraform apply cancels within
a reasonable time of the 5s timeout.

Currently, this test is not canceling the terraform apply as expected. In the
logs you can see that the test takes 1 min rather than ~5s:
```
    --- PASS: TestContext_sleepTimeoutExpired/sleep-0.12.31 (62.13s)
```

```
=== RUN   TestContext_sleepTimeoutExpired/sleep-0.12.31
    util_test.go:113: [INFO] running Terraform command: /var/folders/6y/gy9gggt14379c_k39vwb50lc0000gn/T/terraform_1378921380/terraform apply -no-color -auto-approve -input=false -lock=true -parallelism=10 -refresh=true
    util_test.go:103: CLI Output:
	    // truncated ...
        time_sleep.sleep: Creating...
        time_sleep.sleep: Still creating... [10s elapsed]
        time_sleep.sleep: Still creating... [20s elapsed]
        time_sleep.sleep: Still creating... [30s elapsed]
        time_sleep.sleep: Still creating... [41s elapsed]
        time_sleep.sleep: Still creating... [51s elapsed]
        time_sleep.sleep: Creation complete after 1m0s [id=2022-05-06T17:40:20Z]

        Apply complete! Resources: 1 added, 0 changed, 0 destroyed.
```

Author: lornasong

tfexec/internal/e2etest/errors_test.go

@@ -205,13 +205,21 @@ func TestContext_sleepTimeoutExpired(t *testing.T) {
 		ctx, cancel := context.WithTimeout(ctx, 5*time.Second)
 		defer cancel()
 
-		err = tf.Apply(ctx)
-		if err == nil {
-			t.Fatal("expected error, but didn't find one")
-		}
-
-		if !errors.Is(err, context.DeadlineExceeded) {
-			t.Fatalf("expected context.DeadlineExceeded, got %T %s", err, err)
+		errCh := make(chan error)
+		go func() {
+			err = tf.Apply(ctx)
+			if err != nil {
+				errCh <- err
+			}
+		}()
+
+		select {
+		case err := <-errCh:
+			if !errors.Is(err, context.DeadlineExceeded) {
+				t.Fatalf("expected context.DeadlineExceeded, got %T %s", err, err)
+			}
+		case <-time.After(time.Second * 10):
+			t.Fatal("terraform apply should have canceled and returned in ~5s")
 		}
 	})
 }