Merge remote-tracking branch 'origin/unstable' into capella

Fixing the conflicts involved patching up some of the `block_hash` verification,
the rest will be done as part of https://github.com/sigp/lighthouse/issues/3870

beacon_node/network/src/subnet_service/tests/mod.rs

@@ -2,6 +2,7 @@ use super::*;
 use beacon_chain::{
     builder::{BeaconChainBuilder, Witness},
     eth1_chain::CachingEth1Backend,
+    validator_monitor::DEFAULT_INDIVIDUAL_TRACKING_THRESHOLD,
     BeaconChain,
 };
 use futures::prelude::*;
@@ -75,7 +76,7 @@ impl TestBeaconChain {
                     Duration::from_millis(SLOT_DURATION_MILLIS),
                 ))
                 .shutdown_sender(shutdown_tx)
-                .monitor_validators(true, vec![], log)
+                .monitor_validators(true, vec![], DEFAULT_INDIVIDUAL_TRACKING_THRESHOLD, log)
                 .build()
                 .expect("should build"),
         );