Review swaps

[Peter Lemenkov]

Hello All!
I found out that I am lagging behind my Erlang packaging schedule and
need some help with reviewing. In exchange I'll review your stuck
packages. Pick any of these:

* https://bugzilla.redhat.com/2303752 erlang-rebar3-riak_pb_msgcodegen
- A riak_pb message compiler for rebar3 (a dependency for Riak NoSQL
data-storage).
* https://bugzilla.redhat.com/2303760 erlang-rebar3-gpb - A protobuf
compiler for rebar3
* https://bugzilla.redhat.com/2303917 erlang-riak_core - Distributed
systems infrastructure used by Riak (Re-Review)

Although Erlang sometimes referred as an esoteric language (which is
wrong) we greatly simplified packaging - its mostly done using just
standard macros so spec-files looks quite simple and straightforward.