Check if Tumblebug is initialized or not

[yunkon-kim]

After Tumblebug runs, a user needs to initialize Tumblebug to configure Multi-Cloud info.

This is a manual system configuration process,
so it is not easy to check if the Tumblebug has been initialized during Beetle's readiness check procedure.

Beetle needs to check if Tumblebug is initialized in a slightly different way.

GET /ns/{nsId}/resources/image will be used to support this.