feat(v1.1): Implement /ping endpoint for v1.1

This patch creates a new endpoint /ping in v1.1 API, which is a
clone of the /health endpoint in v1.0. Because a new /health
endpoint will be added in v1.1 to return more detailed KPI of
Marconi server.

Implement blueprint: api-v1.1-ping-endpoint

Change-Id: I486c8a3583fc557c0b0578b0f73a6c6a2a3748b3