Per discussion on slack, it is OK to migrate the validate_drp build for squash results to py3.
Fix kwargs passing (outputPrefix is None error) in validate_drp
validate_drp hsc dataset butler failure
validate_drp decam dataset fails with exit code 6
Change newinstall default to use python3
Change the default python install to python3 for lsstsw deploy
This change should be held off until DM-11300 is merged and we have a known good run of validate_drp under py2, so as not to be juggling multiple changes at once.
lsstsw and newinstall.sh switch to py3 by default today, so I am going to go ahead and switch validate_drp to py3 as well despite the outstanding problems.