Use CLI to configure max instances cache (#5177)

* Use CLI to configure max instances cache

* Fix tests

* Move default value into CLI

* Use SmallVec

* Apply review comments

* Get rid of `SmallVec`

Co-authored-by: Bastian Köcher <git@kchr.de>

substrate/primitives/runtime-interface/test/src/lib.rs

@@ -37,6 +37,7 @@ fn call_wasm_method<HF: HostFunctionsT>(method: &str) -> TestExternalities {
 		Some(8),
 		host_functions,
 		false,
+		8,
 	);
 	executor.call_in_wasm(
 		&WASM_BINARY[..],