Rename config key grind_cache to grind_cache_dir for uniformity
Rename config key grind_cache to grind_cache_dir for uniformity

xiao-chen/dist_test,cloudera/dist_test,umbrant/dist_test,umbrant/dist_test,xiao-chen/dist_test,xiao-chen/dist_test,cloudera/dist_test,cloudera/dist_test,umbrant/dist_test,xiao-chen/dist_test,umbrant/dist_test,cloudera/dist_test