adding zero drive back

some hypervisors will need manual virt-sparsify or equivalent

prepare-ubuntu-18.04-template.sh

@@ -98,6 +98,10 @@ sudo sed -ri '/\sswap\s/s/^#?/#/' /etc/fstab
 # cleans out all of the cloud-init cache / logs - this is mainly cleaning out networking info
 sudo cloud-init clean --logs
 
+# zero out drive
+dd if=/dev/zero of=EMPTY bs=1M status=progress
+rm EMPTY
+fstrim -av
 
 #cleanup shell history
 cat /dev/null > ~/.bash_history && history -c