core: cli flag to disable grandpa (#2105)

* core: cli flag to disable grandpa

* core: fix test service configuration

* Update core/service/test/src/lib.rs

substrate/core/cli/src/params.rs

@@ -220,6 +220,10 @@ pub struct RunCmd {
 	#[structopt(long = "validator")]
 	pub validator: bool,
 
+	/// Disable GRANDPA when running in validator mode
+	#[structopt(long = "no-grandpa")]
+	pub no_grandpa: bool,
+
 	/// Run in light client mode
 	#[structopt(long = "light")]
 	pub light: bool,