Migrate mapred_test to riak_test

This suite had a fragile setup stage that would regularly cause the automated testers to fail. It has been migrated to the following riak_test modules in basho/riak_test#209, where it should be much more predictable:

mapred_notfound_failover
mapred_javascript
mapred_dead_pipe
mapred_buffer_prereduce
mapred_basic_compat