Multitest has errors with reply data

[ethanfrey]

Messages should return the standard x/wasm protobuf format in the data field when returned.

We do that now with instantiate_reply which does the proper proto wrapping, but it is set inside execute_wasm and is overwriten if any submessages return non-empty data on reply

Ideally, we apply this wrapper after all submessages have been returned, but that is a bit tricky with the current logic flow (may need some non-trivial refactoring)

I also noticed that Execute and Migrate messages return the data raw, while there are proto wrappers for both of them.

I will add some failing tests.