Upgrade discovery and restructure task execution (#1693)

* Initial rebase

* Remove old code

* Correct release tests

* Rebase commit

* Remove eth2-testnet dep on eth2libp2p

* Remove crates lost in rebase

* Remove unused dep

beacon_node/timer/Cargo.toml

@@ -12,4 +12,4 @@ tokio = { version = "0.2.22", features = ["full"] }
 slog = "2.5.2"
 parking_lot = "0.11.0"
 futures = "0.3.5"
-environment = { path = "../../lighthouse/environment" }
+task_executor = { path = "../../common/task_executor" }

beacon_node/timer/src/lib.rs

@@ -12,7 +12,7 @@ use tokio::time::{interval_at, Instant};
 
 /// Spawns a timer service which periodically executes tasks for the beacon chain
 pub fn spawn_timer<T: BeaconChainTypes>(
-    executor: environment::TaskExecutor,
+    executor: task_executor::TaskExecutor,
     beacon_chain: Arc<BeaconChain<T>>,
     milliseconds_per_slot: u64,
 ) -> Result<(), &'static str> {