veyron/services/mgmt/suidhelper/impl: set the default uid threshold back to 501 for darwin, now that Cos has updated the 'jenkins' uid on his Mac machine.
veyron/services/mgmt/suidhelper/impl: set the default uid threshold back to 501
for darwin, now that Cos has updated the 'jenkins' uid on his Mac machine.

Change-Id: Iec1265b97f0db0a502b16ef6133ec5465dd3a067

vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref,vanadium/go.ref