Add "pathrows" argument to run_landsat_validation.py

[sharkinsspatial]

For VIIRS investigation purposes, @madhuksridhar would like the ability to run L30 granules using only the input path rows that were used to create the original published granule so that the new output can be exactly compared.

To allow this we'll need some type of allow pathrows argument so that any pathrows not in this list are ignored. This will be the inverse of the explicit ignore argument we have now. This work should be completed on update_validation_viirs branch and then merged to dev.