- QubesVmStorage provides now a default get_config_params() method which should
be enough for all possible Storage implementations.
- When writing a custom Storage implementation, one has just to reimplement the
following methods:
* root_dev_config()
* private_dev_config()
* volatile_dev_config()
- QubesVmStorage provides a default implementation of other_dev_config(),
because it can be shared by all storage implementations