Fixes #3214: Multimap get & remove should return correct collection type

Fixes https://github.com/hazelcast/hazelcast/issues/3214

- Currently multimap get & remove always return list type. With this fix, they should return correct collection type depending on the configuration of multimap's value collection type.
This kind of stuff is hard to read because you have double nested expressions. The following is a lot more readable

```
MultiMapResponse response = new MultiMapResponse(null, getValueCollectionType(container));
getResponseHandler().sendResponse(response)
```

Don't optimize code for writing, but optimize it for reading; since code is read a lot more frequent than it is written.