MNAIO: Implement retries for image downloads

The image downloads may fail, even with aria's built-in
retry mechanism. With this patch we ensure that ansible
will delay and retry again. This improves the chances of
success.

With this we also remove the '--quiet' default parameter
so that we get console output from the task if it does
ultimately fail. This is useful for diagnostic purposes.

Change-Id: Ieed41f06a22effb28463637184980a748791edfe

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

@@ -28,7 +28,6 @@
         --check-integrity true
         --retry-wait=30
         --continue
-        --quiet
   tasks:
     - name: Get the manifest file
       uri:
@@ -56,3 +55,7 @@
 
     - name: Download artifacts
       command: aria2c --input-file=/tmp/aria2c.input {{ aria2c_parameters }}
+      register: _download_artifacts
+      until: _download_artifacts is success
+      retries: 3
+      delay: 30