e2e: Optimize waiting for application to start

We had to switch from
```bash
$ grep -q 'The app is running at:' <(tail -f $tmp_server_log)
```
to

```bash
while true
do
  if grep -q 'The app is running at:' $tmp_server_log; then
    break
  else
    sleep 1
  fi
done
```

I would appreciate a bash expert one-lining this again with cygwin support.