Fix race condition when configuring the qemu save directory

The /var/lib/libvirt/qemu/save directory is not actually created
by the installation of libvirt-bin, it is created by libvirt upon
startup. So if libvirt is slow to initialize and this task runs
before the directory is created, then the next task:
"Check if the qemu save directory is empty" will fail with:
stderr: ls: cannot access /var/lib/libvirt/qemu/save: No such file or directory

Change-Id: I0d035fa6b4eaedebb733fef2126fe9c4f63c2917

tasks/nova_compute_kvm_install.yml

@@ -16,6 +16,9 @@
 - name: Check the state of the default qemu save directory
   stat:
     path: "/var/lib/libvirt/qemu/save"
+  until: _qemu_save_dir.stat.exists | bool
+  retries: 5
+  delay: 10
   register: _qemu_save_dir
 
 - name: Check if the qemu save directory is empty