VC: accept unknown fields in chain spec (#2277)

## Issue Addressed

Closes #2274

## Proposed Changes

* Modify the `YamlConfig` to collect unknown fields into an `extra_fields` map, instead of failing hard.
* Log a debug message if there are extra fields returned to the VC from one of its BNs.

This restores Lighthouse's compatibility with Teku beacon nodes (and therefore Infura)

beacon_node/eth1/src/inner.rs

@@ -53,7 +53,7 @@ impl Inner {
     pub fn from_bytes(bytes: &[u8], config: Config, spec: ChainSpec) -> Result<Self, String> {
         let ssz_cache = SszEth1Cache::from_ssz_bytes(bytes)
             .map_err(|e| format!("Ssz decoding error: {:?}", e))?;
-        Ok(ssz_cache.to_inner(config, spec)?)
+        ssz_cache.to_inner(config, spec)
     }
 
     /// Returns a reference to the specification.

beacon_node/eth2_libp2p/src/behaviour/mod.rs

@@ -36,7 +36,7 @@ use ssz::Encode;
 use std::collections::HashSet;
 use std::fs::File;
 use std::io::Write;
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 use std::{
     collections::VecDeque,
     marker::PhantomData,
@@ -1336,7 +1336,7 @@ impl<TSpec: EthSpec> std::convert::From<Response<TSpec>> for RPCCodedResponse<TS
 }
 
 /// Persist metadata to disk
-pub fn save_metadata_to_disk<E: EthSpec>(dir: &PathBuf, metadata: MetaData<E>, log: &slog::Logger) {
+pub fn save_metadata_to_disk<E: EthSpec>(dir: &Path, metadata: MetaData<E>, log: &slog::Logger) {
     let _ = std::fs::create_dir_all(&dir);
     match File::create(dir.join(METADATA_FILENAME))
         .and_then(|mut f| f.write_all(&metadata.as_ssz_bytes()))

beacon_node/eth2_libp2p/src/service.rs

@@ -474,7 +474,7 @@ fn strip_peer_id(addr: &mut Multiaddr) {
 
 /// Load metadata from persisted file. Return default metadata if loading fails.
 fn load_or_build_metadata<E: EthSpec>(
-    network_dir: &std::path::PathBuf,
+    network_dir: &std::path::Path,
     log: &slog::Logger,
 ) -> MetaData<E> {
     // Default metadata

beacon_node/src/config.rs

@@ -10,7 +10,7 @@ use std::cmp::max;
 use std::fs;
 use std::net::{IpAddr, Ipv4Addr, ToSocketAddrs};
 use std::net::{TcpListener, UdpSocket};
-use std::path::PathBuf;
+use std::path::{Path, PathBuf};
 use std::str::FromStr;
 use types::{ChainSpec, Checkpoint, Epoch, EthSpec, Hash256, PublicKeyBytes, GRAFFITI_BYTES_LEN};
 
@@ -422,7 +422,7 @@ pub fn get_config<E: EthSpec>(
 pub fn set_network_config(
     config: &mut NetworkConfig,
     cli_args: &ArgMatches,
-    data_dir: &PathBuf,
+    data_dir: &Path,
     log: &Logger,
     use_listening_port_as_enr_port_by_default: bool,
 ) -> Result<(), String> {

beacon_node/store/src/hot_cold_store.rs

@@ -660,7 +660,7 @@ impl<E: EthSpec, Hot: ItemStore<E>, Cold: ItemStore<E>> HotColdDB<E, Hot, Cold>
         partial_state.load_historical_roots(&self.cold_db, &self.spec)?;
         partial_state.load_randao_mixes(&self.cold_db, &self.spec)?;
 
-        Ok(partial_state.try_into()?)
+        partial_state.try_into()
     }
 
     /// Load a restore point state by its `restore_point_index`.