Fix plankton shared_from image listing

Commit 469d099 introduced a typo which caused /plankton/shared_images/
to raise an UnboundLocalError.

snf-cyclades-app/synnefo/plankton/backend.py

@@ -342,6 +342,7 @@ class ImageBackend(object):
             # To get shared images, we connect as shared_from member and
             # get the list shared by us
             user = shared_from
+            accounts = [self.user]
         else:
             user = None if public else self.user
             accounts = backend.list_accounts(user)