change celery result backend

docs/install.rst

@@ -46,7 +46,6 @@ Set up default Storage configuration and activate the virtual environment::
 
   $ cat >>/home/cloud/.virtualenvs/storage/bin/postactivate <<END
   export AMQP_URI='amqp://cloud:password@host:5672/circle'
-  export CACHE_URI='pylibmc://$(hostname):11211/'
   END
   $ workon storage
   $ cd ~/storagedriver

storagecelery.py

@@ -16,15 +16,13 @@ if HOSTNAME is None:
                     "Hostname format must be hostname.module.priority.")
 
 AMQP_URI = getenv('AMQP_URI')
-CACHE_URI = getenv('CACHE_URI')
 
 celery = Celery('storagedriver',
                 broker=AMQP_URI,
                 include=['storagedriver'])
 
 celery.conf.update(
-    CELERY_RESULT_BACKEND='cache',
-    CELERY_CACHE_BACKEND=CACHE_URI,
+    CELERY_RESULT_BACKEND='amqp',
     CELERY_TASK_RESULT_EXPIRES=300,
     CELERY_QUEUES=(
         Queue(HOSTNAME, Exchange(