DonorAssignmentQC not emitting plotCommonDonorsFdrDistribution result

[jamesnemesh]

DonorAssignmentStandardAnalysis.R has a function plotCommonDonorsFdrDistribution that is called, but it's missing a print statement so the ggplot is not added to the PDF.

Solution: modify plotCommonDonorsFdrDistribution so the last line is print(p) instead of returning the ggplot2 object.