Fix get_objects to allow filtering

Fix get_objects to allow filtering

At the moment, an attempt to retrieve a list of objects (like qos
policy) and filter by name fails, because get_objects does not use
filters and therefore, upon query by object name, the server replies
with a list of all created objects (instead of a partial list).

Change-Id: I9df9981129b8f3b82e867c8423986f5e0150186b
Partially-Implements: blueprint quantum-qos-api