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/network/src/router/processor.rs

@@ -41,7 +41,7 @@ pub struct Processor<T: BeaconChainTypes> {
 impl<T: BeaconChainTypes> Processor<T> {
     /// Instantiate a `Processor` instance
     pub fn new(
-        executor: environment::TaskExecutor,
+        executor: task_executor::TaskExecutor,
         beacon_chain: Arc<BeaconChain<T>>,
         network_globals: Arc<NetworkGlobals<T::EthSpec>>,
         network_send: mpsc::UnboundedSender<NetworkMessage<T::EthSpec>>,