Notify user on port-forward retries

Motivation: https://chat.google.com/room/AAAAuTCR_1s/905kkZ11Ajo

A user saw errors like the following and assumed port-forwarding was broken:
```
port forwarding deployment-grpc-proxy-idolackrif-partnerfeedwh-server-12600 got terminated: output: Unable to connect to the server: dial tcp 35.246.76.45:443: connect: connection timed out

port forwarding deployment-partnerfeedwh-idolackrif-partnerfeedwh-server-8080 got terminated: output: error: error upgrading connection: error sending request: Post "https://35.246.76.45/api/v1/namespaces/idolackrif-partnerfeedwh-server/pods/partnerfeedwh-6cc9b8fdd5-p9z7j/portforward": dial tcp 35.246.76.45:443: connect: connection timed out
```

When running with `-vdebug`, we discovered that Skaffold had retried the `kubectl port-forward`s and was successful. But the user did not know this, and thought the errors indicates that it was failed.

It would be useful if Skaffold would include output on subsequent retries to alert the user that a new attempt will be made.