Current implementation (or my intention) is as follows:
- riak-cs-multibag is independent of riak-cs-admin (riak-cs-admin does not call it)
- `rebar generage` (or overlay setting in reltool.config) copies riak-cs-multibag script
  regardless oss or ee, but
- oss package does not include it and ee does (by pkg.vars.config generated by rebar.config.script).

(ugly? better way wanted :) )