Fix validator lockfiles (#1586)

## Issue Addressed

- Resolves #1313 

## Proposed Changes

Changes the way we start the validator client and beacon node to ensure that we cleanly drop the validator keystores (which therefore ensures we cleanup their lockfiles).

Previously we were holding the validator keystores in a tokio task that was being forcefully killed (i.e., without `Drop`). Now, we hold them in a task that can gracefully handle a shutdown.

Also, switches the `--strict-lockfiles` flag to `--delete-lockfiles`. This means two things:

1. We are now strict on lockfiles by default (before we weren't).
1. There's a simple way for people delete the lockfiles if they experience a crash.

## Additional Info

I've only given the option to ignore *and* delete lockfiles, not just ignore them. I can't see a strong need for ignore-only but could easily add it, if the need arises.

I've flagged this as `api-breaking` since users that have lockfiles lingering around will be required to supply `--delete-lockfiles` next time they run.

beacon_node/src/lib.rs

@@ -7,7 +7,7 @@ mod config;
 pub use beacon_chain;
 pub use cli::cli_app;
 pub use client::{Client, ClientBuilder, ClientConfig, ClientGenesis};
-pub use config::{get_data_dir, get_eth2_testnet_config, set_network_config};
+pub use config::{get_config, get_data_dir, get_eth2_testnet_config, set_network_config};
 pub use eth2_config::Eth2Config;
 
 use beacon_chain::events::TeeEventHandler;
@@ -17,7 +17,6 @@ use beacon_chain::{
     builder::Witness, eth1_chain::CachingEth1Backend, slot_clock::SystemTimeSlotClock,
 };
 use clap::ArgMatches;
-use config::get_config;
 use environment::RuntimeContext;
 use slog::{info, warn};
 use std::ops::{Deref, DerefMut};
@@ -54,7 +53,7 @@ impl<E: EthSpec> ProductionBeaconNode<E> {
     /// configurations hosted remotely.
     pub async fn new_from_cli(
         context: RuntimeContext<E>,
-        matches: &ArgMatches<'_>,
+        matches: ArgMatches<'static>,
     ) -> Result<Self, String> {
         let client_config = get_config::<E>(
             &matches,