DM-3692 cherry-picked the HSC ticket HSC-966 which allows for a set fraction of stars to be reserved from PSF fitting. Write a unit test to check that this functionality works correctly.
nondeterministic random number seeds in MeasurePsf candidate reservation
HSC backport: Allow for some fraction of PSF Candidates to be reserved from the fitting
Done on DM-9579: https://github.com/LSST/pipe_tasks/commit/e4c3b9bbeb8aa2ef75f4c0fc2a01c0a8835e7f90