Adjust the configuration options, as discussed on the
maria-developers@ mailing list.

The option to hint a transaction to not be replicated in parallel is
now called @@skip_parallel_replication, consistent with
@@skip_replication.

And the --slave-parallel-mode is now simplified to have just one of
the following values:

  none
  minimal
  conservative
  optimistic
  aggressive

This reflects successively harder efforts to find opportunities to run
things in parallel on the slave. It allows to extend the server with
more automatic heuristics in the future without having to introduce a
new configuration option for each and every one.