MNAIO: Log aria2c results

In order to aid in the troubleshooting of download failures,
we set aria2c to produce a log in a configurable location.
Rather than use the default log level of 'debug', which logs
so much information that it affects the host performance due
to the massive amount of IOPS, we set it to 'notice' which
should be sufficient information for debugging most situations.

Change-Id: I67a41026f8e62562a9f3d9c08512f5da2a27f3dc

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

@@ -22,12 +22,15 @@
     - download-vms
   vars:
     aria2c_parameters: >-
+        --log-level=notice
         --allow-overwrite=true
         --conditional-get=true
         --max-connection-per-server=4
         --check-integrity true
         --retry-wait=30
         --continue
+    aria2c_log_path: >-
+        /tmp
   tasks:
     - name: Get the manifest file
       uri:
@@ -54,7 +57,11 @@
         dest: "/tmp/aria2c.input"
 
     - name: Download artifacts
-      command: aria2c --input-file=/tmp/aria2c.input {{ aria2c_parameters }}
+      command: >-
+        aria2c
+        --input-file=/tmp/aria2c.input
+        --log={{ aria2c_log_path }}/aria2c.log
+        {{ aria2c_parameters }}
       register: _download_artifacts
       until: _download_artifacts is success
       retries: 3