Only write child pids to journal for bluepill daemonized processes

When using bluepill to monitor a self daemonizing process such as unicorn, it will append the child pids to the bluepill journal. If a custom restart command is specified, the journal is never cleared and new child pids will be added to the journal without removing the old ones. Since the ```start_process``` method only append pids to the journal when bluepill is daemonizing the process, we should be consistent and do the same for the ```refresh_children!``` method.