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>

beacon_node/eth2_libp2p/src/behaviour/mod.rs

@@ -983,7 +983,14 @@ impl<TSpec: EthSpec> NetworkBehaviour for Behaviour<TSpec> {
         };
 
         if let Some(goodbye_reason) = goodbye_reason {
-            debug!(self.log, "Disconnecting newly connected peer"; "peer_id" => peer_id.to_string(), "reason" => goodbye_reason.to_string());
+            match goodbye_reason {
+                GoodbyeReason::Banned => {
+                    debug!(self.log, "Disconnecting newly connected peer"; "peer_id" => peer_id.to_string(), "reason" => goodbye_reason.to_string())
+                }
+                _ => {
+                    trace!(self.log, "Disconnecting newly connected peer"; "peer_id" => peer_id.to_string(), "reason" => goodbye_reason.to_string())
+                }
+            }
             self.peers_to_dc
                 .push_back((peer_id.clone(), Some(goodbye_reason)));
             // NOTE: We don't inform the peer manager that this peer is disconnecting. It is simply
@@ -1079,6 +1086,8 @@ impl<TSpec: EthSpec> NetworkBehaviour for Behaviour<TSpec> {
             // Inform the behaviour.
             delegate_to_behaviours!(self, inject_disconnected, peer_id);
 
+            debug!(self.log, "Peer disconnected"; "peer_id" => %peer_id);
+
             // Decrement the PEERS_PER_CLIENT metric
             if let Some(kind) = self
                 .network_globals