Fix simulator failed runs (#2181)

## Issue Addressed

N/A

## Proposed Changes

Another attempt at fixing simulator issues for `eth1-sim`. 
The `LocalValidatorClient` here blocks till genesis has occurred. 
e4b62139d7/testing/simulator/src/local_network.rs (L145-L150)

Due to this, only the first validator(validator_0) starts before genesis. The remaining 3 vc's in the simulation start only after genesis. This was probably causing issues with missing the duties and eventually the proposal for slot 1.

This PR spawns each `LocalValidatorClient` in it's own tokio task to allow the remaining validators to start before genesis.

## Additional Info

Please provide any additional information. For example, future considerations
or information useful for reviewers.

testing/simulator/src/eth1_sim.rs

@@ -13,6 +13,7 @@ use rayon::prelude::*;
 use std::cmp::max;
 use std::net::{IpAddr, Ipv4Addr};
 use std::time::Duration;
+use tokio::time::sleep;
 use types::{Epoch, EthSpec, MainnetEthSpec};
 
 pub fn run_eth1_sim(matches: &ArgMatches) -> Result<(), String> {
@@ -123,7 +124,7 @@ pub fn run_eth1_sim(matches: &ArgMatches) -> Result<(), String> {
         /*
          * Create a new `LocalNetwork` with one beacon node.
          */
-        let network = LocalNetwork::new(context, beacon_config.clone()).await?;
+        let network = LocalNetwork::new(context.clone(), beacon_config.clone()).await?;
 
         /*
          * One by one, add beacon nodes to the network.
@@ -139,12 +140,26 @@ pub fn run_eth1_sim(matches: &ArgMatches) -> Result<(), String> {
         /*
          * One by one, add validators to the network.
          */
+
+        let executor = context.executor.clone();
         for (i, files) in validator_files.into_iter().enumerate() {
-            network
-                .add_validator_client(testing_validator_config(), i, files, i % 2 == 0)
-                .await?;
+            let network_1 = network.clone();
+            executor.spawn(
+                async move {
+                    println!("Adding validator client {}", i);
+                    network_1
+                        .add_validator_client(testing_validator_config(), i, files, i % 2 == 0)
+                        .await
+                        .expect("should add validator");
+                },
+                "vc",
+            );
         }
 
+        let duration_to_genesis = network.duration_to_genesis().await;
+        println!("Duration to genesis: {}", duration_to_genesis.as_secs());
+        sleep(duration_to_genesis).await;
+
         /*
          * Start the checks that ensure the network performs as expected.
          *