Adds --no-validator CLI flag (#3348)

* Implement `is_validator` for offchain-workers

* Introduce `--no-validator` flag

* Don't run babe/grandpa/im-online when `--no-validator` is given

* Fixes compilation

* Bump spec version

* Improve error handling in executor

* Add missing extern function

* Revert making error public

* Remove `--no-validator` CLI

substrate/core/cli/src/lib.rs

@@ -436,6 +436,8 @@ where
 		),
 	};
 
+	let is_dev = cli.shared_params.dev;
+
 	let role = if cli.light {
 		service::Roles::LIGHT
 	} else {
@@ -462,8 +464,6 @@ where
 	config.roles = role;
 	config.disable_grandpa = cli.no_grandpa;
 
-	let is_dev = cli.shared_params.dev;
-
 	let client_id = config.client_id();
 	fill_network_configuration(
 		cli.network_config,