Use rustls instead of openssl

With rustls it's easier to embed the root CA certificates inside
the compiled binary itself using the webpki-roots crate. We need to
do this because it's the easiest way of getting TLS certificate
validation working inside the initramfs where /etc/ssl/certs or
else does not exist.

Cargo.toml

@@ -14,7 +14,7 @@ hex = "0.4.2"
 anyhow = "1.0.32"
 clap = "2.33.3"
 psutil = { git = "https://github.com/leo-lb/rust-psutil", branch = "lle-bout/impl-serde", version = "3.1.0", features = ["serde"] }
-reqwest = { version = "0.10.7", features = ["blocking", "native-tls-vendored"] }
+reqwest = { version = "0.10.7", default-features = false, features = ["blocking", "rustls-tls"] }
 rmp-serde = "0.14.4"
 nix = "0.18.0"
 serde = { version = "1.0.115", features = ["derive"] }