Allow passing a custom database when creating the Service (#3957)

* Put the DB configuration in an enum

* Allow passing a custom database to client-db

* Clean-ups in client-db

* Fix client tests

* Fix service tests

* Hopefully fix tests for good this time 😩

* Address review

substrate/core/service/test/src/lib.rs

@@ -29,6 +29,7 @@ use service::{
 	AbstractService,
 	ChainSpec,
 	Configuration,
+	config::DatabaseConfig,
 	Roles,
 	Error,
 };
@@ -170,8 +171,10 @@ fn node_config<G, E: Clone> (
 		network: network_config,
 		keystore_path: root.join("key"),
 		keystore_password: None,
-		database_path: root.join("db"),
-		database_cache_size: None,
+		database: DatabaseConfig::Path {
+			path: root.join("db"),
+			cache_size: None
+		},
 		state_cache_size: 16777216,
 		state_cache_child_ratio: None,
 		pruning: Default::default(),