Make nova-network use FixedIP object for vif queries and bulk create

This makes nova-network use FixedIP for querying by virtual interface
and for bulk-creating IP records in the database. These two unrelated
changes were both smallish and thus combined into this patch to
reduce the queue depth for this series.

Related to blueprint nova-network-objects

Change-Id: I93d6ce32b0960173d70f6ec32d889ae91e2849bb
Merge "Make nova-network use FixedIP object for vif queries and bulk create"