start adding tracing spans to internals (#478)

We've adopted `tracing` for diagnostics, but currently, it is just being
used as a drop-in replacement for the `log` crate. Ideally, we would
want to start emitting more structured diagnostics, using `tracing`'s
`Span`s and structured key-value fields.

A lot of the logging in `h2` is already written in a style that imitates
the formatting of structured key-value logs, but as textual log
messages. Migrating the logs to structured `tracing` events therefore is
pretty easy to do. I've also started adding spans, mostly in the read
path.

Finally, I've updated the tests to use `tracing` rather than
`env_logger`. The tracing setup happens in a macro, so that a span for
each test with the test's name can be generated and entered. This will
make the test output easier to read if multiple tests are run
concurrently with `--nocapture`.

Signed-off-by: Eliza Weisman <eliza@buoyant.io>

src/client.rs

@@ -149,6 +149,7 @@ use std::task::{Context, Poll};
 use std::time::Duration;
 use std::usize;
 use tokio::io::{AsyncRead, AsyncWrite, AsyncWriteExt};
+use tracing_futures::Instrument;
 
 /// Initializes new HTTP/2.0 streams on a connection by sending a request.
 ///
@@ -1115,7 +1116,10 @@ where
     T: AsyncRead + AsyncWrite + Unpin,
 {
     let builder = Builder::new();
-    builder.handshake(io).await
+    builder
+        .handshake(io)
+        .instrument(tracing::trace_span!("client_handshake", io = %std::any::type_name::<T>()))
+        .await
 }
 
 // ===== impl Connection =====
@@ -1438,6 +1442,8 @@ impl Peer {
 impl proto::Peer for Peer {
     type Poll = Response<()>;
 
+    const NAME: &'static str = "Client";
+
     fn r#dyn() -> proto::DynPeer {
         proto::DynPeer::Client
     }