hostname: hostname doesn't accept invalid utf-8

[Devel08]

$ sudo cargo run -p uu_hostname $'\xFF'

thread 'main' (40469) panicked at library/std/src/env.rs:871:51:
called `Result::unwrap()` on an `Err` value: "\xFF"
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

[oech3]

Cannot repro:

$ target/debug/hostname $'\xFF'
hostname: failed to set hostname: Permission denied
$ target/debug/hostname a
hostname: failed to set hostname: Permission denied

However, we probably should avoid lossy conversion.

[Devel08]

changing hostname works only with root privilleges

[xtqqczze]

Invalid UTF-8 host names may be a bad idea for interoperability, but POSIX does not forbid them.