Cleanup required variables checks for all containers

This allows Kubernetes to reschedule containers in case a required
variable is missing, for example when the Kubernetes pod is started
before the service.

The checks were cleaned using the following method:
  * remove duplicates
  * remove check for variables that get a default value in the same file
  * check for all variables used in the file
  * check for required services when it is obvious.

Change-Id: Ib7e0530c410c61f828d36efe8925a20dc9781eab