The client-example has a confusing return for the `download` function.

[kairoaraujo]

Description of issue:
The client-example has a confusing return for the download function.
The return mixes the error and flows handling.

Current behavior:
Currently, it returns a bool.

• If a target file is downloaded it returns True
• If there is an exception in the code it returns False
• if a target file is not found it returns True

python-tuf/examples/client_example/client_example.py

Line 78 in c12be48

return False

Expected behavior:
The return code only manages the exceptions. However, there is no use for the current return.

[kairoaraujo]

Thread in Slack channel: https://cloud-native.slack.com/archives/C01GT17AC5D/p1657718611407839

[jku]

I think this may get fixed in #2193

[jku]

should be fixed by now?