qinj_vth_scan yaml output and bug handling

Outputs charge injection data generated using --qinj_vth_scan to yaml file instead of pickle, and retries charge injection in rare cases of failure up to 10 times. Note retry occurs at DAC level, so reaching the ten-time failure limit will not invalidate all data for a particular QSel value (assuming, of course, more than one DAC value in sweep). Also prints error that occurred before retry.