Remove stdout argument from coredns log

According to the documentation the first argument to log is either a
domain or a '.' (dot). The current setting of 'log stdout' appears to
blackhole query logs. The default output of log is stdout so the
argument would not be necessary.

Removing `stdout` allows coredns to send query logs to stdout.

Reference: https://coredns.io/plugins/log/

Change-Id: I7837015c37eb58ba43ff42cc8b647c717fa1c650
(cherry picked from commit e4e0843)

Author: Travis Holton

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

@@ -74,7 +74,7 @@ data:
   Corefile: |
     .:53 {
         errors
-        log stdout
+        log
         health
         kubernetes ${DNS_CLUSTER_DOMAIN} ${PORTAL_NETWORK_CIDR} ${PODS_NETWORK_CIDR} {
            pods verified

magnum/drivers/k8s_coreos_v1/templates/fragments/enable-coredns.yaml

@@ -48,7 +48,7 @@ write_files:
         Corefile: |
           .:53 {
               errors
-              log stdout
+              log
               health
               kubernetes ${DNS_CLUSTER_DOMAIN} {
                 cidrs ${PORTAL_NETWORK_CIDR}