export riak_pipe:zero_part/1 for use from riak_test
remove tests that were migrated to riak_test

these tests were moved to riak_test as part of commit
a63c30993e93db8c9f3c2e912b5fcab238cdb635 in that repo,
in pull request riak_test#143
move validate_test_ from riak_pipe to riak_pipe_fitting

These tests all exercise riak_pipe_fitting, and don't need to startup a
cluster to do so. Since there are no more tests that need to startup a
cluster, remove that code as well.
Merge pull request #62 from branch 'bwf-riak_test'