Enable result set filtering for all objects

Given that result sets can be quite large for nontrivial installations, the Sahara API needs to be able to support filtering of result sets. Ideally, query parameters can be passed in on the REST URL with the "?name=value" syntax and the sahara service will restrict the result sets by the given filters (which might just be field values, or possibly things related to pagination/max results).

Each object type should be able to be filtered by any of the fields contained in it. We should be able to specify parameters for pagination (page, results per page) and maxumum result count.

There are corresponding changes planned for python-saharaclient and the Sahara Horizon UI. Here are links to those blueprints:
python-saharaclient: https://blueprints.launchpad.net/python-saharaclient/+spec/enable-result-filtering
horizon: https://blueprints.launchpad.net/horizon/+spec/data-processing-table-filtering