Merge branch 'stable-2.14' into stable-2.15

* stable-2.14:
  Allow to disable health check endpoint
  AbstractIndexRestApiServlet: Log operation type in lower case
  Make debug logging consistent in forwarder and cache servlet
  Use Logger's built-in string formatting
  Restrict endpoints to change health status to admins
  Add unit tests for HealthServlet
  Initial implementation of health servlet

Change-Id: Idb83c5beac343490b8cb7ea031b2fb40863c7f25