The function only uses one public function of `gossiper` (`is_alive`)
and is used only in one place in `storage_proxy`.
Make it a static function private to the `storage_proxy` module.
The function used a `default_random_engine` field in `gossiper` for
generating random numbers. Turn this field into a static `thread_local`
variable inside the function - no other `gossiper` members used the
field.
566e5f2a4f