Update to tokio 1.1 (#2172)

## Issue Addressed

resolves #2129
resolves #2099 
addresses some of #1712
unblocks #2076
unblocks #2153 

## Proposed Changes

- Updates all the dependencies mentioned in #2129, except for web3. They haven't merged their tokio 1.0 update because they are waiting on some dependencies of their own. Since we only use web3 in tests, I think updating it in a separate issue is fine. If they are able to merge soon though, I can update in this PR. 

- Updates `tokio_util` to 0.6.2 and `bytes` to 1.0.1.

- We haven't made a discv5 release since merging tokio 1.0 updates so I'm using a commit rather than release atm. **Edit:** I think we should merge an update of `tokio_util` to 0.6.2 into discv5 before this release because it has panic fixes in `DelayQueue`  --> PR in discv5:  https://github.com/sigp/discv5/pull/58

## Additional Info

tokio 1.0 changes that required some changes in lighthouse:

- `interval.next().await.is_some()` -> `interval.tick().await`
- `sleep` future is now `!Unpin` -> https://github.com/tokio-rs/tokio/issues/3028
- `try_recv` has been temporarily removed from `mpsc` -> https://github.com/tokio-rs/tokio/issues/3350
- stream features have moved to `tokio-stream` and `broadcast::Receiver::into_stream()` has been temporarily removed -> `https://github.com/tokio-rs/tokio/issues/2870
- I've copied over the `BroadcastStream` wrapper from this PR, but can update to use `tokio-stream` once it's merged https://github.com/tokio-rs/tokio/pull/3384

Co-authored-by: realbigsean <seananderson33@gmail.com>

boot_node/src/server.rs

@@ -5,7 +5,6 @@ use eth2_libp2p::{
     discv5::{enr::NodeId, Discv5, Discv5ConfigBuilder, Discv5Event},
     EnrExt, Eth2Enr,
 };
-use futures::prelude::*;
 use slog::info;
 use types::EthSpec;
 
@@ -78,7 +77,7 @@ pub async fn run<T: EthSpec>(config: BootNodeConfig<T>, log: slog::Logger) {
     // listen for events
     loop {
         tokio::select! {
-            _ = metric_interval.next() => {
+            _ = metric_interval.tick() => {
                 // display server metrics
                 let metrics = discv5.metrics();
                 info!(log, "Server metrics"; "connected_peers" => discv5.connected_peers(), "active_sessions" => metrics.active_sessions, "requests/s" => format!("{:.2}", metrics.unsolicited_requests_per_second));