Improve tokio task execution (#1181)

* Add logging on shutdown

* Replace tokio::spawn with handle.spawn

* Upgrade tokio

* Add a task executor

* Beacon chain tasks use task executor

* Validator client tasks use task executor

* Rename runtime_handle to executor

* Add duration histograms; minor fixes

* Cleanup

* Fix logs

* Fix tests

* Remove random file

* Get enr dependency instead of libp2p

* Address some review comments

* Libp2p takes a TaskExecutor

* Ugly fix libp2p tests

* Move TaskExecutor to own file

* Upgrade Dockerfile rust version

* Minor fixes

* Revert "Ugly fix libp2p tests"

This reverts commit 58d4bb690f.

* Pretty fix libp2p tests

* Add spawn_without_exit; change Counter to Gauge

* Tidy

* Move log from RuntimeContext to TaskExecutor

* Fix errors

* Replace histogram with int_gauge for async tasks

* Fix todo

* Fix memory leak in test by exiting all spawned tasks at the end

beacon_node/eth2-libp2p/Cargo.toml

@@ -35,6 +35,7 @@ tokio-util = { version = "0.3.1", features = ["codec", "compat"] }
 # Patched for quick updates
 discv5 = { git = "https://github.com/sigp/discv5", rev = "7b3bd40591b62b8c002ffdb85de008aa9f82e2e5" }
 tiny-keccak = "2.0.2"
+environment = { path = "../../lighthouse/environment" }
 libp2p-tcp = { version = "0.19.1", default-features = false, features = ["tokio"] }
 
 [dependencies.libp2p]
@@ -49,3 +50,4 @@ slog-stdlog = "4.0.0"
 slog-term = "2.5.0"
 slog-async = "2.5.0"
 tempdir = "0.3.7"
+exit-future = "0.2.0"