OTP 17.0

We can defer 17.0 adoption on Riak server, but we can't defer on Erlang client because many of Erlang applications which are using Riak may want to catch up with latest OTP version (or want to use maps).

This is still ongoing work. This depends on:

- https://github.com/basho/riak_pb/pull/89
- https://github.com/basho/meck/pull/1