[Run2_2018_prompt] Pileup dataset checking for get_mcm.py

Created by: aperloff

Update get_mcm.py to find and print the validity of the pileup dataset. If the pu dataset is incorrect the dataset is added to the unfinished cartegory and a notation is made. This commit also adds some additional samples to the default get_mcm dictionary. This is a port of #349.