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/network/src/service.rs

@@ -266,7 +266,7 @@ fn spawn_service<T: BeaconChainTypes>(
                     info!(service.log, "Network service shutdown");
                     return;
                 }
-                _ = service.metrics_update.next() => {
+                _ = service.metrics_update.tick() => {
                     // update various network metrics
                     metric_update_counter +=1;
                     if metric_update_counter % T::EthSpec::default_spec().seconds_per_slot == 0 {
@@ -283,7 +283,7 @@ fn spawn_service<T: BeaconChainTypes>(
                     metrics::update_sync_metrics(&service.network_globals);
 
                 }
-                _ = service.gossipsub_parameter_update.next() => {
+                _ = service.gossipsub_parameter_update.tick() => {
                     if let Ok(slot) = service.beacon_chain.slot() {
                         if let Some(active_validators) = service.beacon_chain.with_head(|head| {
                                 Ok::<_, BeaconChainError>(