Setting the "prometheus: kube-prometheus" label selector for mariadb-galera
ServiceMonitor object is invalid since mariadb-galera-metrics service has
common labels assigned.
Without this change Prometheus (in kube-prometheus-stack) does not select
the mariadb-galera-metrics service for scraping and relevant target is
not created.
Change-Id: I64dfe83ff7fb448125f8726cf3ca33048ced04a8
Issue-ID: OOM-2925
Signed-off-by: Bartek Grzybowski <b.grzybowski@partner.samsung.com>