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/http_metrics/Cargo.toml

@@ -8,7 +8,7 @@ edition = "2018"
 
 [dependencies]
 prometheus = "0.10.0"
-warp = { git = "https://github.com/paulhauner/warp", branch = "cors-wildcard" }
+warp = { git = "https://github.com/sigp/warp ", branch = "lighthouse" }
 serde = { version = "1.0.116", features = ["derive"] }
 slog = "2.5.2"
 beacon_chain = { path = "../beacon_chain" }
@@ -22,7 +22,8 @@ lighthouse_version = { path = "../../common/lighthouse_version" }
 warp_utils = { path = "../../common/warp_utils" }
 
 [dev-dependencies]
-tokio = { version = "0.2.22", features = ["sync"] }
+tokio = { version = "0.3.2", features = ["sync"] }
 reqwest = { version = "0.10.8", features = ["json"] }
 environment = { path = "../../lighthouse/environment" }
 types = { path = "../../consensus/types" }
+tokio-compat-02 = "0.1"