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/tests/test.rs

@@ -1,14 +1,11 @@
 #![cfg(test)]
 
-//TODO: Drop compat library once reqwest and other libraries update to tokio 0.3
-
 use beacon_chain::StateSkipConfig;
 use node_test_rig::{
     environment::{Environment, EnvironmentBuilder},
     eth2::types::StateId,
     testing_client_config, LocalBeaconNode,
 };
-use tokio_compat_02::FutureExt;
 use types::{EthSpec, MinimalEthSpec, Slot};
 
 fn env_builder() -> EnvironmentBuilder<MinimalEthSpec> {
@@ -44,11 +41,7 @@ fn http_server_genesis_state() {
 
     let api_state = env
         .runtime()
-        .block_on(
-            remote_node
-                .get_debug_beacon_states(StateId::Slot(Slot::new(0)))
-                .compat(),
-        )
+        .block_on(remote_node.get_debug_beacon_states(StateId::Slot(Slot::new(0))))
         .expect("should fetch state from http api")
         .unwrap()
         .data;