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, where it should be much more predictable:

mapred_notfound_failover
mapred_javascript
mapred_dead_pipe
mapred_buffer_prereduce
mapred_basic_compat
Merge pull request #489 from branch 'bwf-move-mapred-test'