Send elector._leadertime as status update uptime instead of elector._starttime

Using elector._starttime as basis for uptime in the status update will
cause the wrong value to be compared to _elector_startup_tolerance in
runner::_update_elector_state().

This can cause unexpected behavior, eg. temporary demotion of a master
node when quorum is lost for an interval shorter than
_elector_startup_tolerance.