agent_uuid "hostname" generate a new UUID

The Python Keylime agent have the option to set `agent_uuid = hostname`, to set the FQDN as the UUID agent. The Rust version do not implement this feature (but is documented in [keylime.conf](https://github.com/keylime/rust-keylime/blob/master/keylime.conf#L63-L64))

I am looking for a Rust crate that can here, but so far no one is following how Python works (`socket.getfqdn` that use `gethostname` and `gethostbyaddr` from POSIX `netdb`).

Start with the agent_uuid option documented in keylime.conf and locate the Rust configuration and agent UUID handling. Compare the requested hostname mode with Python's socket.getfqdn behavior, then verify that setting agent_uuid to hostname produces the expected FQDN-based UUID.

Written by the indexing model from the issue text.