node: exit on GRANDPA voter or BABE authoring error (#3353)

* node: exit on GRANDPA voter or BABE authoring error

* node: exit process with non-zero return code when service fails

* service: rename infallible task to essential task

* service: revert field name changes

* core: fix service testnet

substrate/node/src/main.rs

@@ -55,7 +55,7 @@ fn main() {
 	};
 
 	if let Err(e) = cli::run(::std::env::args(), Exit, version) {
-		eprintln!("Error starting the node: {}\n\n{:?}", e, e);
+		eprintln!("Fatal error: {}\n\n{:?}", e, e);
 		std::process::exit(1)
 	}
 }