Simplification streamable commands

[srgg]

Please ensure the following is present in your PR:

• Unit tests for your change
• Integration tests (if applicable)

Pull requests that are small and limited in scope are most welcome.

[alexmoore]

Most of these changes look good (and needed).
The only thing that stands out are these two unchecked suppressions. We're ignoring the type system here, which always feels bad for some reason. Could we make these abstract methods, and then provide subclasses where I == CoreI and/or R == CoreR, and use those where necessary?

Sort of like what I did with the ImmediateCoreFutureAdapter: https://github.com/basho/riak-java-client/pull/677/files#diff-1c6f3b6c65d8e0eeaee247ff938a349bR70 ?

[srgg]

I hate usage of whatever suppression, therefore it took some time from me to make a decision. The idea was to avoid the necessity of creating additional object such as ImmediateCoreFutureAdapter.SameQueryInfo and use Method References whenever it is possible. And also to reduce complexity I've added these default implementation that covers default scenario that doesn't require response/info conversion.

But later I realized that it might have sense to introduce another class to handle this specific case and GenericRiakComand should extend it.

[alexmoore]

+1