Adding harvesting code for SIM and DIGI and changing cmsDriver option.

I added harvesting code for sim and digi. 
- The harvestor make efficiency plots only. 
- Occupancy plots are generated at validation.

cmsDriver options were changed, I will modify twiki page for digi validation and harvesting.
- On gemCustom.py, remove digi_validation and digi_prevalidation.
- The digi validtion is added to genvalid_all. So, we should use "VALIDATION:genvalid_all" to run digi validation.
- The digi harvestor is added to genHarvesting. "HARVESTING:genHarvesting"  is used on cmsDriver.