Remove unrwaps/expects in qos client CLI

[emostov]

The client CLI uses unwraps/expects everywhere. In order to make the lower level functions more re-usable across contexts we should have them returns errors instead of panicking. Additionally, it probably makes sense to exit with with a non-zero status code instead of panicking. I think not panicking should give us a better chance of clearing sensitive memory before exiting.

ref: #154 (review)

[emostov]

Importantly, panics should also be removed from verify_attestation_doc_against_user_input.