Child storage tests and genesis fix. (#3185)

* Using child storage, (srml-support only), test failing .

* fix simple tests.

* Enumerable by requiring owned struct (previous form only allow
&'static).
Broken tests are from genesis init.

* implement for_child_keys_with_prefix

* indent

* clear_child_prefix fix.

* clear_child_prefix fix 2.

* fix for storage_impl, if/when allowing child and not child this could be
reverted.

* Fix lot of urlinked child genesis, still need to look upon actual
genesis srml module code.
Probably still a lot of broken code needing debugging.

* switch well_known_key to their associated module child trie.
Fix a genesis init (balance).
Complete some testing.
Comment some tests before using.

* fixing test runtime child keys

* latest commit fix broken genesis init

* fix system balances child name.

* Important fix: storage_root from test externalities need children (it is
already the case for ext).

* executive root with child calculation

* Avoid empty trie on test ext.

* Symetric removal of key for system.

* commenting changes related tests.

* Remove child module specifics.

* fix issues.

* fix some formatting

* fix bench and bump runtime

* Remove extend_storage_overlays, assimilate_storage do the same as is
proper considering srml macro.

* Fix warning for assimilate.

* Removing kill as they do not impact any test cases.

* Use tuple of storage map instead of two parameters. This changes the
behavior of decl_storage genesis build closure (breaking api).

* Do not use build storage before assimilate.

* fix error

* Update core/state-machine/src/backend.rs

substrate/srml/support/src/lib.rs

@@ -327,7 +327,7 @@ mod tests {
 	}
 
 	fn new_test_ext() -> runtime_io::TestExternalities<Blake2Hasher> {
-		GenesisConfig::default().build_storage().unwrap().0.into()
+		GenesisConfig::default().build_storage().unwrap().into()
 	}
 
 	type Map = Data;

substrate/srml/support/src/metadata.rs

@@ -324,7 +324,7 @@ mod tests {
 				StorageMethod : Option<u32>;
 			}
 			add_extra_genesis {
-				build(|_, _, _| {});
+				build(|_, _| {});
 			}
 		}
 	}

substrate/srml/support/src/storage/storage_items.rs

@@ -379,7 +379,7 @@ mod tests {
 			COMPLEXTYPE3: ([u32;25]);
 		}
 		add_extra_genesis {
-			build(|_, _, _| {});
+			build(|_, _| {});
 		}
 	}
 
@@ -755,7 +755,7 @@ mod test2 {
 		add_extra_genesis {
 			config(_marker) : ::std::marker::PhantomData<T>;
 			config(extra_field) : u32 = 32;
-			build(|_, _, _| {});
+			build(|_, _| {});
 		}
 	}