INTERNAL: Add an arcus_zk_initalized function

[ing-eoking]

🔗 Related Issue

• jam2in/arcus-works#551

⌨️ What I did

• zk_integrated 판별을 memcached.c 가 아닌 arcus_zk 모듈을 통해 가능하게 끔 변경합니다.

🎯 To Do

• [x] zkensemble 명령어 테스트 진행 (모두 이전과 동일)
  • -z 옵션이 주어진 경우

    # Client
    zkensemble get
    0.0.0.0:50000 

  • -z 옵션이 주어지지 않은 경우

    zkensemble get
    ERROR not using ZooKeeper

  • mc_pause 상태

    # Server
    zk connection closed by mc_pause.
    Failed to get the ZooKeeper ensemble list. Invalid ZK handle.
    # Client
    zkensemble get
    ERROR failed to get the ensemble address
    zkensemble rejoin
    Successfully rejoined

[ing-eoking]

@jhpark816

수정되었습니다.