Upgrade to tokio 0.3 (#1839)

## Description

This PR updates Lighthouse to tokio 0.3. It includes a number of dependency updates and some structural changes as to how we create and spawn tasks.

This also brings with it a number of various improvements:

- Discv5 update
- Libp2p update
- Fix for recompilation issues
- Improved UPnP port mapping handling
- Futures dependency update
- Log downgrade to traces for rejecting peers when we've reached our max



Co-authored-by: blacktemplar <blacktemplar@a1.net>

testing/eth1_test_rig/src/lib.rs

@@ -13,7 +13,7 @@ use deposit_contract::{
 use futures::compat::Future01CompatExt;
 use ganache::GanacheInstance;
 use std::time::Duration;
-use tokio::time::delay_for;
+use tokio::time::sleep;
 use types::DepositData;
 use types::{test_utils::generate_deterministic_keypair, EthSpec, Hash256, Keypair, Signature};
 use web3::contract::{Contract, Options};
@@ -220,7 +220,7 @@ impl DepositContract {
     /// Peforms many deposits, each preceded by a delay.
     pub async fn deposit_multiple(&self, deposits: Vec<DelayThenDeposit>) -> Result<(), String> {
         for deposit in deposits.into_iter() {
-            delay_for(deposit.delay).await;
+            sleep(deposit.delay).await;
             self.deposit_async(deposit.deposit).await?;
         }
         Ok(())