Show gcloud output more frequently than one line at a time

When deploying an App Engine standard application, the output pauses for a while after

```
[INFO] GCLOUD: File upload done.
```

After a minute or so we get the line

```
[INFO] GCLOUD: Updating service [default]..............................done.
```

I believe the `gcloud` command is outputting the `.`s as a progress-indicator, but this does not work well with the plugin, which only displayed the line after it was completely done.