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>

validator_client/src/attestation_service.rs

@@ -6,7 +6,6 @@ use crate::{
 };
 use environment::RuntimeContext;
 use futures::future::FutureExt;
-use futures::StreamExt;
 use slog::{crit, error, info, trace};
 use slot_clock::SlotClock;
 use std::collections::HashMap;
@@ -149,7 +148,8 @@ impl<T: SlotClock + 'static, E: EthSpec> AttestationService<T, E> {
         let executor = self.context.executor.clone();
 
         let interval_fut = async move {
-            while interval.next().await.is_some() {
+            loop {
+                interval.tick().await;
                 let log = self.context.log();
 
                 if let Err(e) = self.spawn_attestation_tasks(slot_duration) {