Add ParasSudoWrapper to test-runtime and bring back register_parachain to test-service (#1811)

* Make register/deregister parachain dispatchables

This makes `register_parachain` and `deregister_parachain` of
`Registrar` dispatchables.

Besides that it brings back the functionality of the test node to
register a parachain.

* Fix tests

* PR review comments

polkadot/runtime/parachains/src/paras.rs

@@ -176,7 +176,6 @@ pub struct ParaGenesisArgs {
 	pub parachain: bool,
 }
 
-
 decl_storage! {
 	trait Store for Module<T: Trait> as Paras {
 		/// All parachains. Ordered ascending by ParaId. Parathreads are not included.