Add meck's passthrough option option

Meck uses original module attributes and riakc_pb_socket has
deprecated one.

  -deprecated({get_index,'_', eventually}).

Without passthrough option, no get_index function is created
and the error occurs in R16B03

{compile_forms,
    {error,
        [{[],[{75,erl_lint,{bad_deprecated,{get_index,'_'}}}]}],
        [{[],
          [{75,erl_lint,{undefined_behaviour,[gen_server]}}]}]}}}
Refactor: refrect review comments

- function name change
- better comment sentences
- space chage
Use master branch in riak_cs_multibag repository