TT#54511 Switch Install CD default DNS server to public one

Sipwise DNS servers in LDC will be turned off soonish,
also new DNS servers in GCloud will NOT be available for public usage.
We have to use some public DNS servers.

Change-Id: I1c5cb78b90da18e893658417a6886b7b4f81fa0d

grub.cfg

@@ -50,7 +50,7 @@ menuentry "Install Debian/stretch 64bit" {
 
 menuentry "Install Debian/stretch 64bit - Puppet" {
   echo 'Loading kernel...'
-  linux /boot/%SHORT_NAME%/vmlinuz live-media-path=/live/%GRML_NAME%/ boot=live bootid=%BOOTID% apm=power-off mgag200.modeset=0 vga=791 quiet nomce net.ifnames=0 nongcp ssh=sipwise debianrelease=stretch scripts puppetenv=production dns=92.42.136.30,92.42.136.31 ip=10.15.20.123::10.15.20.1:255.255.255.0:puppet-client42:eth0:off 
+  linux /boot/%SHORT_NAME%/vmlinuz live-media-path=/live/%GRML_NAME%/ boot=live bootid=%BOOTID% apm=power-off mgag200.modeset=0 vga=791 quiet nomce net.ifnames=0 nongcp ssh=sipwise debianrelease=stretch scripts puppetenv=production dns=1.1.1.1,8.8.8.8 ip=10.15.20.123::10.15.20.1:255.255.255.0:puppet-client42:eth0:off 
   echo 'Loading initrd...'
   initrd /boot/%SHORT_NAME%/initrd.img
 }

isolinux.cfg

@@ -122,7 +122,7 @@ label stretch
 label stretchpuppet
   menu label Install Debian/stretch  64bit - Puppet
   kernel /boot/%SHORT_NAME%/vmlinuz
-  append initrd=/boot/%SHORT_NAME%/initrd.img live-media-path=/live/%GRML_NAME%/ boot=live bootid=%BOOTID% apm=power-off mgag200.modeset=0 vga=791 quiet nomce net.ifnames=0 nongcp ssh=sipwise debianrelease=stretch scripts puppetenv=production dns=92.42.136.30,92.42.136.31 ip=10.15.20.123::10.15.20.1:255.255.255.0:puppet-client42:eth0:off 
+  append initrd=/boot/%SHORT_NAME%/initrd.img live-media-path=/live/%GRML_NAME%/ boot=live bootid=%BOOTID% apm=power-off mgag200.modeset=0 vga=791 quiet nomce net.ifnames=0 nongcp ssh=sipwise debianrelease=stretch scripts puppetenv=production dns=1.1.1.1,8.8.8.8 ip=10.15.20.123::10.15.20.1:255.255.255.0:puppet-client42:eth0:off 
 
   text help
                                      Install Debian stretch, 64bit using