Make Test Helpers no_std Compatible (#823)

* Use `sp-application-crypto` when generating test justifications

* Try to justifications tests compiling

* Try using `ed25519_dalek` for justification creation

* Small cleanup

* Correctly generate a Keypair

The public key didn't correspond to what would be derived
with the given private key.

* Remove enum index hack

* Clean up test account helper functions

* Fix tests in `pallet-finality-verifier`

* Get `pallet-substrate-bridge` tests compiling again

* Use the correct keyring in justification tests

* Clean up Keyring related code a bit

* Appease Clippy

* Remove unused import

* Use keyring variants directly

* Remove unecessary From implementation

bridges/primitives/header-chain/tests/justification.rs

@@ -23,12 +23,7 @@ use codec::Encode;
 type TestHeader = sp_runtime::testing::Header;
 
 fn make_justification_for_header_1() -> GrandpaJustification<TestHeader> {
-	make_justification_for_header(
-		&test_header(1),
-		TEST_GRANDPA_ROUND,
-		TEST_GRANDPA_SET_ID,
-		&authority_list(),
-	)
+	make_justification_for_header(&test_header(1), TEST_GRANDPA_ROUND, TEST_GRANDPA_SET_ID, &keyring())
 }
 
 #[test]