veyron/services/mgmt/suidhelper/impl: setgid before uid
veyron/services/mgmt/suidhelper/impl: setgid before uid

In the suidhelper, set the gid before setting uid in case the uid does
not have permissions to change its gid.

Change-Id: I3cfe8d455d85e0854c188690718ccc22839529f4

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