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