Incorrect parameters passed

Incorrect parameters sequence is passed to
delete_from_backend() method.

delete_from_backend(self.admin_context, uri) in this
method uri should be the first argument instead of
self.admin_context.

Closes-Bug:1378640
Change-Id: Iebc30bad4f201dde75f2e8fe9b56e20c007c772b
Merge "Incorrect parameters passed"