Start the plasma store.

def start_plasma_store(self):
        """Start the plasma store."""
        stdout_file, stderr_file = self.new_log_files("plasma_store")
        process_info = ray.services.start_plasma_store(
            stdout_file=stdout_file,
            stderr_file=stderr_file,
            object_store_memory=self._ray_params.object_store_memory,
            plasma_directory=self._ray_params.plasma_directory,
            huge_pages=self._ray_params.huge_pages,
            plasma_store_socket_name=self._plasma_store_socket_name)
        assert (
            ray_constants.PROCESS_TYPE_PLASMA_STORE not in self.all_processes)
        self.all_processes[ray_constants.PROCESS_TYPE_PLASMA_STORE] = [
            process_info
        ]