Increase verbosity on bots during setup and other minor cleanup (#19526)

The verbosity change is to help track down timeouts that currently look like:

```
C:\Windows\Temp\flutter sdk>call bin\flutter.bat config --no-analytics
Checking Dart SDK version...
Downloading Dart SDK from Flutter engine c5a63d28bf3735569c8187753bc490d8351a8363...
Unzipping Dart SDK...
Updating flutter tool...
```