Only create storage instances when required, not on import.

This drastically speeds up startup times for anything that imports all
models (which is pretty much anything in Django). It saves having to
connect to the remote storage, in particular, until it's required.

queued_storage/backend.py

@@ -11,15 +11,27 @@ class QueuedRemoteStorage(Storage):
 
     def __init__(self, local, remote, cache_prefix=QUEUED_REMOTE_STORAGE_CACHE_KEY_PREFIX, task=None):
         self.local_class = local
-        self.local = get_storage_class(self.local_class)()
         self.remote_class = remote
-        self.remote = get_storage_class(self.remote_class)()
         self.cache_prefix = cache_prefix
+        self._local_instance = None
+        self._remote_instance = None
 
         # allow users to override the task that uploads the image to the remote
         # server
         self.task = task or SaveToRemoteTask
 
+    @property
+    def local(self):
+        if self._local_instance is None:
+            self._local_instance = get_storage_class(self.local_class)()
+        return self._local_instance
+
+    @property
+    def remote(self):
+        if self._remote_instance is None:
+            self._remote_instance = get_storage_class(self.remote_class)()
+        return self._remote_instance
+
     def get_storage(self, name):
         cache_result = cache.get(self.get_cache_key(name))