dashboard: use failed property to detect failed disks

circle/dashboard/templates/dashboard/_disk-list-element.html

 {% load i18n %}
 {% load sizefieldtags %}
 
-<i class="{% if d.is_downloading %}icon-refresh icon-spin{% else %}icon-file{% if not d.ready %}" style="color: #d9534f;{% endif %}{% endif %}"></i> 
+<i class="{% if d.is_downloading %}icon-refresh icon-spin{% else %}icon-file{% if d.failed %}" style="color: #d9534f;{% endif %}{% endif %}"></i> 
 {{ d.name }} (#{{ d.id }}) - 
 {% if not d.is_downloading %}
-  {% if d.ready %}
-    {{ d.size|filesize }}
+  {% if not d.failed %}
+    {% if d.size %}{{ d.size|filesize }}{% endif %}
   {% else %}
-    <div class="label label-danger">failed</div>
+  <div class="label label-danger"{% if user.is_superuser %} title="{{ d.get_latest_activity_result }}"{% endif %}>failed</div>
   {% endif %}
 {% else %}<span class="disk-list-disk-percentage" data-disk-pk="{{ d.pk }}">{{ d.get_download_percentage }}</span>%{% endif %}
 <a href="{% url "dashboard.views.disk-remove" pk=d.pk %}?next={{ request.path }}" 

circle/storage/models.py

@@ -193,6 +193,9 @@ class Disk(AclBase, TimeStampedModel):
         result = celery.AsyncResult(id=task)
         return result.info.get("percent")
 
+    def get_latest_activity_result(self):
+        return self.activity_log.latest("pk").result
+
     @property
     def is_deletable(self):
         """True if the associated file can be deleted.