Port ip-echo-server to tokio 0.3 (bp #14345) (#14350)

* Port ip-echo-server to tokio 0.3

(cherry picked from commit fb6c660cfd)

# Conflicts:
#	net-utils/Cargo.toml

* Update Cargo.toml

Co-authored-by: Michael Vines <mvines@gmail.com>

core/src/validator.rs

@@ -756,7 +756,7 @@ impl Validator {
         self.completed_data_sets_service
             .join()
             .expect("completed_data_sets_service");
-        self.ip_echo_server.shutdown_now();
+        self.ip_echo_server.shutdown_background();
     }
 }