[CERN] Fix prometheus scrape configuration
cherry picked from : https://review.openstack.org/#/c/509791/
Make prometheus configuration compatible with 1.7.3 or greater. The new config matches the one in the pormetheus kubernetes example [1] minus the configuration for ingress that we don't deploy.
[1] https://github.com/prometheus/prometheus/blob/master/documentation/examples/prometheus-kubernetes.yml Closes-Bug: #1719187
Change-Id: Ied8b8d8fb610e5ecba18e37f98dd1a4c9bddbf30