Nova-net: fix server side deallocate_for_instance()

Client side of the network RPC API sets 'requested_networks'
parameter in deallocate_for_instance() call,
while server side expected 'fixed_ips' parameter.
This patch fixes server side so it handles 'requested_networks'

Closes-Bug: #1350355

Change-Id: If9554a2e98397c5e63e929e1606d99dd2328262c
Merge "Nova-net: fix server side deallocate_for_instance()"