Change yz_security test to determine priv directory via rt:priv_dir
Change riak_test modules to build yz_driver as needed

Change the appropriate riak_test modules to build the yokozuna
basho_bench driver as needed. The driver can still be used for
independent basho_bench testing, but no extra setup is required in
order to run riak_test with the yokozuna tests.
Test updates to avoid nondeterminism in riak_test execution

Changes to avoid some problems with nondeterminism with execution
of the yokozuna riak_test modules.
Update TESTING.md to reflect the update riak_test procedures
Add repo clone instruction to TESTING docs
Use yz_rt:bb_driver_setup for aae_test
Merge pull request #351 from basho/refactor/normalize-riak-test-execution

Normalize riak_test execution process

Reviewed-by: coderoshi