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>

beacon_node/timer/Cargo.toml

@@ -8,7 +8,7 @@ edition = "2018"
 beacon_chain =  { path = "../beacon_chain" }
 types = { path = "../../consensus/types" }
 slot_clock = { path = "../../common/slot_clock" }
-tokio = { version = "0.3.2", features = ["full"] }
+tokio = { version = "1.1.0", features = ["full"] }
 slog = "2.5.2"
 parking_lot = "0.11.0"
 futures = "0.3.7"

beacon_node/timer/src/lib.rs

@@ -3,7 +3,6 @@
 //! This service allows task execution on the beacon node for various functionality.
 
 use beacon_chain::{BeaconChain, BeaconChainTypes};
-use futures::stream::StreamExt;
 use slog::info;
 use slot_clock::SlotClock;
 use std::sync::Arc;
@@ -26,7 +25,8 @@ pub fn spawn_timer<T: BeaconChainTypes>(
     // Warning: `interval_at` panics if `seconds_per_slot` = 0.
     let mut interval = interval_at(start_instant, Duration::from_secs(seconds_per_slot));
     let timer_future = async move {
-        while interval.next().await.is_some() {
+        loop {
+            interval.tick().await;
             beacon_chain.per_slot_task();
         }
     };