baremetal: Add script to configure local DNS

This was previously done with an option to dhclient, but this doesn't
work when doing DHCPv6.  Switch to a script run by NetworkManager to do
the same thing.

This matches the same approach moved to by the MCO in this PR:

openshift/machine-config-operator#1396

data/data/bootstrap/baremetal/files/etc/NetworkManager/dispatcher.d/30-local-dns-prepender

@@ -0,0 +1,20 @@
+#!/bin/bash
+IFACE=$1
+STATUS=$2
+case "$STATUS" in
+    up)
+    logger -s "NM local-dns-prepender triggered by ${1} ${2}."
+    DNS_IP="127.0.0.1"
+    set +e
+    logger -s "NM local-dns-prepender: Checking if local DNS IP is the first entry in resolv.conf"
+    if grep nameserver /etc/resolv.conf | head -n 1 | grep -q "$DNS_IP" ; then
+        logger -s "NM local-dns-prepender: local DNS IP already is the first entry in resolv.conf"
+        exit 0
+    else
+        logger -s "NM local-dns-prepender: Looking for '# Generated by NetworkManager' in /etc/resolv.conf to place 'nameserver $DNS_IP'"
+        sed -i "/^# Generated by.*$/a nameserver $DNS_IP" /etc/resolv.conf
+    fi
+    ;;
+    *)
+    ;;
+esac

pkg/asset/ignition/bootstrap/bootstrap.go

@@ -275,7 +275,7 @@ func (a *Bootstrap) addStorageFiles(base string, uri string, templateData *boots
 
 	var mode int
 	appendToFile := false
-	if path.Base(path.Dir(uri)) == "bin" {
+	if path.Base(path.Dir(uri)) == "bin" || filename == "30-local-dns-prepender" {
 		mode = 0555
 	} else if filename == "motd" {
 		mode = 0644