[NGRINDER-710] Add easy cluster mode
[NGRINDER-713] Reduce the file and db access
[NGRINDER-710] Add more configuration error detect logic
[NGRINDER-690] Fix bugs which was created when rest api is created.
[NGRINDER-703] Fix wrong description.
[NGRINDER-710] Add easy cluster mode
[NGRINDER-713] Remove the unncessary local agent db query.