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>

lcli/Cargo.toml

@@ -20,7 +20,7 @@ types = { path = "../consensus/types" }
 state_processing = { path = "../consensus/state_processing" }
 eth2_ssz = "0.1.2"
 regex = "1.3.9"
-futures = { version = "0.3.5", features = ["compat"] }
+futures = { version = "0.3.7", features = ["compat"] }
 environment = { path = "../lighthouse/environment" }
 web3 = "0.11.0"
 eth2_testnet_config = { path = "../common/eth2_testnet_config" }
@@ -28,7 +28,7 @@ dirs = "3.0.1"
 genesis = { path = "../beacon_node/genesis" }
 deposit_contract = { path = "../common/deposit_contract" }
 tree_hash = "0.1.1"
-tokio = { version = "0.2.22", features = ["full"] }
+tokio = { version = "0.3.2", features = ["full"] }
 clap_utils = { path = "../common/clap_utils" }
 eth2_libp2p = { path = "../beacon_node/eth2_libp2p" }
 validator_dir = { path = "../common/validator_dir", features = ["insecure_keys"] }
@@ -36,3 +36,4 @@ rand = "0.7.3"
 eth2_keystore = { path = "../crypto/eth2_keystore" }
 lighthouse_version = { path = "../common/lighthouse_version" }
 directory = { path = "../common/directory" }
+tokio-compat-02 = "0.1"