GCP: Update /etc/hosts file when ClusterHostedDNS is enable

Append /etc/hosts files with entries to resolve cluster api and
api-int URLS. /etc/hosts will provide resolution for these URLs
until kubelet joins the cluster and runs its CoreDNS pod which
will then take over resolution of those 2 URLs

templates/common/gcp/files/usr-local-bin-update-etc-hosts.yaml

@@ -0,0 +1,11 @@
+mode: 0755
+path: "/usr/local/bin/update-etc-hosts"
+contents:
+  inline: |
+    #!/bin/bash
+    etc_hosts_config_filename="/etc/hosts/conf.d/etc-hosts.conf"
+    if [ ! -f "$etc_hosts_config_filename" ]; then
+      exit 0
+    fi
+    cat /etc/hosts/conf.d/etc-hosts.conf >> /etc/hosts
+    echo "Done updating /etc/hosts"

templates/common/gcp/units/gcp-update-etc-hosts.service.yaml

@@ -0,0 +1,44 @@
+name: gcp-update-etc-hosts.service
+enabled: {{if and (eq .Infra.Status.PlatformStatus.Type "GCP") (.Infra.Status.PlatformStatus.GCP) (.Infra.Status.PlatformStatus.GCP.CloudLoadBalancerConfig) (eq .Infra.Status.PlatformStatus.GCP.CloudLoadBalancerConfig.DNSType "ClusterHosted") }}true{{else}}false{{end}}
+contents: |
+  [Unit]
+  Description=Update Default GCP /etc/hosts
+  # We don't need to do this on the firstboot
+  After=firstboot-osupdate.target
+  # Wait for NetworkManager to report it's online
+  After=NetworkManager-wait-online.service
+  # Run before kubelet
+  Before=kubelet-dependencies.target
+
+  [Service]
+  # Need oneshot to delay kubelet
+  Type=oneshot
+  ExecStart=/bin/bash -c " \
+{{ if and (eq .Infra.Status.PlatformStatus.Type "GCP") (.Infra.Status.PlatformStatus.GCP) (.Infra.Status.PlatformStatus.GCP.CloudLoadBalancerConfig) (eq .Infra.Status.PlatformStatus.GCP.CloudLoadBalancerConfig.DNSType "ClusterHosted") }}
+  {{ $apiLBIPs := cloudPlatformAPILoadBalancerIPs .}}
+  {{ $apiIntLBIPs := cloudPlatformAPIIntLoadBalancerIPs .}}
+{{ else }}
+  exit 0
+{{ end }}
+  if [ -z "${apiIntLBIPs}" ]; then
+    # We don't have API-Int LB IPs. Nothing to do here.
+    exit 0
+  fi
+  if [ -z "${apiLBIPs}" ]; then
+    # Private cluster
+    apiLBIPs=${apiIntLBIPs}
+  fi
+  apiServerURL={{ .Infra.Status.APIServerURL }}
+  apiServerIntURL={{ .Infra.Status.APIServerInternalURL }}
+  # Add the/etc/hosts configuration file
+  mkdir -p /etc/hosts/conf.d
+  cat <<EOF | tee /etc/hosts/conf.d/etc-hosts.conf
+  # Added by OpenShift
+  ${apiLBIPs[0]}    ${apiServerURL}
+  ${apiIntLBIPs[0]}    ${apiServerIntURL} 
+  EOF
+  # Update /etc/hosts
+  /usr/local/bin/update-etc-hosts"
+
+  [Install]
+  RequiredBy=kubelet-dependencies.target