Ease Riak Setup and usage

[fkrause98]

There are some things that we can do better and that would be good to address as we're planning to provide
an elixir library for riak, like:

• Avoiding weird Erlang macros like this one:

handle_handoff_command(?FOLD_REQ{foldfun=FoldFun, acc0=Acc0}, _Sender,
                       State = #{data := Data}) ->
  log("Received fold request for handoff", State),
  Result = maps:fold(FoldFun, Acc0, Data),
  {reply, Result, State};

Currently I'm using this as a workaround:

  require Record

  Record.defrecord(
    :fold_req_v2,
    :riak_core_fold_req_v2,
    Record.extract(:riak_core_fold_req_v2, from_lib: "riak_core/include/riak_core_vnode.hrl")
  )

• See If we can make the VMaster setup more straight forward.
• See If we can make the FSM Coverage setup more straight forward.
• Maybe provide an Elixir specific VNode behaviour that wraps the original one.