fix(BA-438): Libc version not parsed on image without metadata label

[kyujin-cho]

Follow-up PR of #3173 and #2582. On #3173 we forced Entrypoint value as sh to force override the value set from the image, but it caused another shell script evaluation error. Along with that it seems that we can just let container use docker system's default value by passing [""] as the Entrypoint config.

Checklist: (if applicable)

• Milestone metadata specifying the target backport version
• Mention to the original issue
• Installer updates including:
  • Fixtures for db schema changes
  • New mandatory config options
• Update of end-to-end CLI integration tests in ai.backend.test
• API server-client counterparts (e.g., manager API -> client SDK)
• Test case(s) to:
  • Demonstrate the difference of before/after
  • Demonstrate the flow of abstract/conceptual models with a concrete implementation
• Documentation
  • Contents in the docs directory
  • docstrings in public interfaces and type annotations