Add parameters field for protectable instances API

Now the resource instances only can be queried from defaut region. If there are
several regions in one site/keystone, we can not query resource instances
from different region endpoint. We may need a parameter for the region name.

The scene of database protection: If we want to use Protectable Instances API to
query database instances from vendor's backup software. We must pass some parameters
about authentication to the RESTfull API of vendor's backup software.

I think we should add a dict type parameter to Protectable Instances API. The key
and value in parameter, which is needed for implementing some Protectable plugins.