[cern] Set coredns cache to 900 secs

The DNS service comlained to users for high load. Per docs, let's put it to 15 mins. https://service-dns.web.cern.ch/faq.asp#caching https://coredns.io/plugins/cache/

Change-Id: I88fe0fc168f516f933ebab59eaa30019de00ab06 Signed-off-by: Spyros Trigazis spyridon.trigazis@cern.ch

magnum/drivers/common/templates/kubernetes/fragments/core-dns-service.sh

@@ -78,7 +78,7 @@ data:
         }
         prometheus :9153
         forward . /etc/resolv.conf
-        cache 30
+        cache 900
         loop
         reload
         loadbalance