Validator on-boarding docs (#656)

* Add first draft of validator onboarding

* Update docs

* Add documentation link to main README

* Continue docs development

* Update book readme

* Update docs

* Allow vc to run without testnet subcommand

* Small change to onboarding docs

* Tidy CLI help messages

* Update docs

* Add check to val client see if beacon node is synced

* Add notifier service to validator client

* Re-order onboarding steps

* Update deposit contract address

* Update testnet dir

* Add note about public eth1 node

* Set default eth1 endpoint to sigp

* Fix broken test

* Try fix eth1 cache locking

* Be more specific about eth1 endpoint

* Increase gas limit for deposit

* Fix default deposit amount

beacon_node/eth1/src/service.rs

@@ -306,8 +306,7 @@ impl Service {
         let log = self.log.clone();
         let update_interval = Duration::from_millis(self.config().auto_update_interval_millis);
 
-        loop_fn((), move |()| {
-            let exit = exit.clone();
+        let loop_future = loop_fn((), move |()| {
             let service = service.clone();
             let log_a = log.clone();
             let log_b = log.clone();
@@ -344,16 +343,11 @@ impl Service {
                         );
                     }
                     // Do not break the loop if there is an timer failure.
-                    Ok(())
+                    Ok(Loop::Continue(()))
                 })
-                .map(move |_| {
-                    if exit.is_live() {
-                        Loop::Continue(())
-                    } else {
-                        Loop::Break(())
-                    }
-                })
-        })
+        });
+
+        exit.until(loop_future).map(|_: Option<()>| ())
     }
 
     /// Contacts the remote eth1 node and attempts to import deposit logs up to the configured