Rewrite tests with a hyper server instead of raw TCP

This makes the tests much less brittle, by not depending on the exact
order of the HTTP headers, nor always requiring to check for every
single header.

tests/support/mod.rs

@@ -1,2 +1,6 @@
-#[macro_use]
 pub mod server;
+
+// TODO: remove once done converting to new support server?
+#[allow(unused)]
+pub static DEFAULT_USER_AGENT: &'static str =
+    concat!(env!("CARGO_PKG_NAME"), "/", env!("CARGO_PKG_VERSION"));