Don't build basho_bench as part of verify.sh

The riak tests now use the `basho_bench` RT config which should point
to a local working copy of basho bench. Not building basho bench can
save a lot of time.
Speed up the RS migration test

Up the concurrency and lower the tick on the Yokozuna side.
Merge pull request #256 from basho/refactor/rz/shorter-verify

Speedup verify