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 58d4bb690f52de28d893943b7504d2d0c6621429.

* 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/src/lib.rs

@@ -58,7 +58,7 @@ impl<E: EthSpec> ProductionBeaconNode<E> {
             &matches,
             &context.eth2_config.spec_constants,
             &context.eth2_config().spec,
-            context.log.clone(),
+            context.log().clone(),
         )?;
         Self::new(context, client_config).await
     }
@@ -75,7 +75,7 @@ impl<E: EthSpec> ProductionBeaconNode<E> {
         let client_config_1 = client_config.clone();
         let client_genesis = client_config.genesis.clone();
         let store_config = client_config.store.clone();
-        let log = context.log.clone();
+        let log = context.log().clone();
 
         let db_path = client_config.create_db_path()?;
         let freezer_db_path_res = client_config.create_freezer_db_path();