Increase support for independent swift storage

Currently, freezer can only store backup data to swift media which is tightly coupled with the OpenStack environment and use the same authentication system (keystone) with nova and cinder etc. Independent swift storage media should be supported by freezer when the swift media was not deployed in the environment, so that freezer users will have more choices to backup there resource.

Implementation thoughts:
1. When specify ‘--auth-url’, ‘--username’ and ‘--password’ in the command, we will use the specify values to create swift client.
2. By default, we will use the old method to create swift client.