Fix for systemd-resolved DNS incompatibility

This problem occurs because kube-dns on systems using systemd-resolved
copy 127.0.0.53 from the host's /etc/resolv.conf.

Since 127.0.0.53 is a loopback address, dns queries never get past
kube-dns causing our conformance tests to fail on DNS related issues.

More discussion here: kubernetes/kubernetes#45828

Related issues:
kubernetes/kubeadm#787
kubernetes/kubeadm#273
kubernetes/kubeadm#845

The upstream fix is now in v1.11.

Without the fix, the kubedns and dnsmasq containers would copy the host's `/etc/resolv.conf`:
```
\# This file is managed by man:systemd-resolved(8). Do not edit.
\#
\# This is a dynamic resolv.conf file for connecting local clients to the
\# internal DNS stub resolver of systemd-resolved. This file lists all
\# configured search domains.
\#
\# Run "systemd-resolve --status" to see details about the uplink DNS servers
\# currently in use.
\#
\# Third party programs must not access this file directly, but only through the
\# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,
\# replace this symlink by a static file or a different symlink.
\#
\# See man:systemd-resolved.service(8) for details about the supported modes of
\# operation for /etc/resolv.conf.

nameserver 127.0.0.53
search platform9.sys
```

After the fix:
```
\# This file is managed by man:systemd-resolved(8). Do not edit.
\#
\# This is a dynamic resolv.conf file for connecting local clients directly to
\# all known uplink DNS servers. This file lists all configured search domains.
\#
\# Third party programs must not access this file directly, but only through the
\# symlink at /etc/resolv.conf. To manage man:resolv.conf(5) in a different way,
\# replace this symlink by a static file or a different symlink.
\#
\# See man:systemd-resolved.service(8) for details about the supported modes of
\# operation for /etc/resolv.conf.

nameserver 10.105.16.2
nameserver 10.105.16.4
search platform9.sys
```

Author: vannrt

constants/constants.go

@@ -75,7 +75,7 @@ const (
 	NodeadmKubeletSystemdDropinFilename = "20-nodeadm.conf"
 	NodeadmKubeletSystemdDropinTemplate = `[Service]
 Environment="KUBELET_DNS_ARGS=--cluster-dns={{ .ClusterDNS }} --cluster-domain={{ .ClusterDomain }}"
-Environment="KUBELET_EXTRA_ARGS=--max-pods={{ .MaxPods }} --fail-swap-on={{ .FailSwapOn }} --hostname-override={{ .HostnameOverride }} --kube-api-qps={{ .KubeAPIQPS }} --kube-api-burst={{ .KubeAPIBurst }} --feature-gates={{ .FeatureGates}} --eviction-hard={{ .EvictionHard }} --cpu-manager-policy={{ .CPUManagerPolicy }} --kube-reserved={{ .KubeReservedCPU }}"
+Environment="KUBELET_EXTRA_ARGS=--resolv-conf=/run/systemd/resolve/resolv.conf --max-pods={{ .MaxPods }} --fail-swap-on={{ .FailSwapOn }} --hostname-override={{ .HostnameOverride }} --kube-api-qps={{ .KubeAPIQPS }} --kube-api-burst={{ .KubeAPIBurst }} --feature-gates={{ .FeatureGates}} --eviction-hard={{ .EvictionHard }} --cpu-manager-policy={{ .CPUManagerPolicy }} --kube-reserved={{ .KubeReservedCPU }}"
 `
 )