Enforce query order for getting VIFs by instance

When spawn VM with multiple nics, during the phase of VM network allocations
using nova-network, the networks pass into driver layer will get reordered
by vifs queried by instance. We have to enforce the query order with vif
creation order rather than rely on the database backend's order.

Change-Id: I51333cc82c03e20d89d3ea548ff164fe71b5ba26
Merge "Enforce query order for getting VIFs by instance"