set coredns as default for kube-up eployments

cluster/gce/config-default.sh

@@ -254,7 +254,7 @@ fi
 
 # Optional: Install cluster DNS.
 # Set CLUSTER_DNS_CORE_DNS to 'true' to install CoreDNS instead of kube-dns.
-CLUSTER_DNS_CORE_DNS="${CLUSTER_DNS_CORE_DNS:-false}"
+CLUSTER_DNS_CORE_DNS="${CLUSTER_DNS_CORE_DNS:-true}"
 ENABLE_CLUSTER_DNS="${KUBE_ENABLE_CLUSTER_DNS:-true}"
 DNS_SERVER_IP="${KUBE_DNS_SERVER_IP:-10.0.0.10}"
 DNS_DOMAIN="${KUBE_DNS_DOMAIN:-cluster.local}"

cluster/gce/config-test.sh

@@ -261,7 +261,7 @@ fi
 
 # Optional: Install cluster DNS.
 # Set CLUSTER_DNS_CORE_DNS to 'true' to install CoreDNS instead of kube-dns.
-CLUSTER_DNS_CORE_DNS="${CLUSTER_DNS_CORE_DNS:-false}"
+CLUSTER_DNS_CORE_DNS="${CLUSTER_DNS_CORE_DNS:-true}"
 ENABLE_CLUSTER_DNS="${KUBE_ENABLE_CLUSTER_DNS:-true}"
 DNS_SERVER_IP="10.0.0.10"
 DNS_DOMAIN="cluster.local"

cluster/gce/util.sh

@@ -848,7 +848,7 @@ ENABLE_RESCHEDULER: $(yaml-quote ${ENABLE_RESCHEDULER:-false})
 LOGGING_DESTINATION: $(yaml-quote ${LOGGING_DESTINATION:-})
 ELASTICSEARCH_LOGGING_REPLICAS: $(yaml-quote ${ELASTICSEARCH_LOGGING_REPLICAS:-})
 ENABLE_CLUSTER_DNS: $(yaml-quote ${ENABLE_CLUSTER_DNS:-false})
-CLUSTER_DNS_CORE_DNS: $(yaml-quote ${CLUSTER_DNS_CORE_DNS:-false})
+CLUSTER_DNS_CORE_DNS: $(yaml-quote ${CLUSTER_DNS_CORE_DNS:-true})
 DNS_SERVER_IP: $(yaml-quote ${DNS_SERVER_IP:-})
 DNS_DOMAIN: $(yaml-quote ${DNS_DOMAIN:-})
 ENABLE_DNS_HORIZONTAL_AUTOSCALER: $(yaml-quote ${ENABLE_DNS_HORIZONTAL_AUTOSCALER:-false})