base directory cannot exec env.sh ,case env.sh script dir not right,

[Hodoryu]

base -> run.py ->start->start_tasks_in_cluster function, input params "case " `s value not right.
env_dir = os.path.join(
config.FLAGPERF_PATH, "benchmarks", case, config.VENDOR)
env_dir ：cannot find dir ,

[shh2000]

thanks for report, you can see if #710 can be a solution