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/node/cli/res/flaming-fir.json

@@ -21,7 +21,7 @@
 	"protocolId": "fir",
 	"consensusEngine": null,
 	"genesis": {
-		"raw": {
+		"raw": [{
 			"0xbc3717660105a864bd63dcd430de64128d58bd0917fa8dd75aee827cf086e19c": "0x0000c16ff28623000000000000000000",
 			"0x8f9a319405d14f3953657373696f6e204b65794f776e6572343a73657373696f6e3a6b657973a6e391e5d17627fa5aaa7a76b39ebee4b139bff595608fe41aea21aa7ea48053": "0x68655684472b743e456907b398d3a44c113f189e56d1bbfd55e889e295dfde78",
 			"0x7eb7a404bf7e3466c3f6c5914e25edfaab48b1e24fd29ea5a94deaaa1aba80e6": "0x0c0001547ff0ab649283a7ae01dbc2eb73932eba2fb09075e9485ff369082a2ff38d65019c7a2ee14e565db0c69f78c7b4cd839fbf52b607d867e9e9c5a79042898a0d12",
@@ -99,6 +99,8 @@
 			"0x717a2ee9c64ad3424e10e4461ec08296": "0x0000000001000000000000000100000000000000010000000000000001000000000000000100000000000000010000000000000001000000000000008700000000000000af0000000000000001000000000000000100000000000000040000000000010010000000004000000020000000",
 			"0xf186665804ca50670311307912458ce448d82cb96e7e4fe71df38c283a8720f4": "0x9c7a2ee14e565db0c69f78c7b4cd839fbf52b607d867e9e9c5a79042898a0d120f0000c16ff286230f0000c16ff2862300",
 			"0x6e4ab2ac5a7cf9b1829eacc84a75bde0804be01fc31c9419ea72407f50a33384": "0xf26cdb14b5aec7b2789fd5ca80f979cef3761897ae1f37ffb3e154cbcc1c2663"
-		}
+		},
+		{
+		}]
 	}
 }