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/beacon_chain/src/eth1_chain.rs

@@ -1,4 +1,5 @@
 use crate::metrics;
+use environment::TaskExecutor;
 use eth1::{Config as Eth1Config, Eth1Block, Service as HttpService};
 use eth2_hashing::hash;
 use slog::{debug, error, trace, Logger};
@@ -285,10 +286,8 @@ impl<T: EthSpec, S: Store<T>> CachingEth1Backend<T, S> {
     }
 
     /// Starts the routine which connects to the external eth1 node and updates the caches.
-    pub fn start(&self, exit: tokio::sync::oneshot::Receiver<()>) {
-        // don't need to spawn as a task is being spawned in auto_update
-        // TODO: check if this is correct
-        HttpService::auto_update(self.core.clone(), exit);
+    pub fn start(&self, handle: TaskExecutor) {
+        HttpService::auto_update(self.core.clone(), handle);
     }
 
     /// Instantiates `self` from an existing service.