MNAIO: Compress the disk image when saving it

When we save the VM disks, we now use compression to prepare
the base disk so that it reduces the base disk file sizes to
a much smaller base. For the infra hosts this reduces the file
from ~23GB to ~8GB. Once this is done, we then also create a
copy-on-write image in the original disk's place so that the
VM can be booted up to verify functionality or continue work
without having to re-run the 'deploy-vms' playbook.

Change-Id: If95b71d8625b4d5b2a036cec13952e4fd73cecd4

multi-node-aio/playbooks/save-vms.yml

@@ -46,13 +46,14 @@
         - hostvars[item]['server_vm'] | default(false) | bool
       with_items: "{{ groups['pxe_servers'] }}"
 
-    - name: Save VM Disk Image
+    - name: Commit, compress and save VM Disk Image and prepare new copy-on-write image
       shell: |
         if [[ -e {{ hostvars[item]['server_hostname'] }}.img ]]; then
           if [[ -e {{ hostvars[item]['server_hostname'] }}-base.img ]]; then
             qemu-img commit {{ hostvars[item]['server_hostname'] }}.img
           else
-            mv {{ hostvars[item]['server_hostname'] }}.img {{ hostvars[item]['server_hostname'] }}-base.img
+            qemu-img convert -O qcow2 -c {{ hostvars[item]['server_hostname'] }}.img {{ hostvars[item]['server_hostname'] }}-base.img
+            qemu-img create -f qcow2 -b {{ hostvars[item]['server_hostname'] }}-base.img {{ hostvars[item]['server_hostname'] }}.img
           fi
           exit 2
         fi