I was getting an {error, enoent} on riak_test setup

See gist here https://gist.github.com/russelldb/356d2735b52fffa1c2e7

This patch fixes it for me. If no-one else has this problem then
this probably isn't the fix.
Merge pull request #401 from basho/maybe_bug/rdb/full-conf-path

I was getting an {error, enoent} on riak_test setup