fixed_ips by vif does not raise

It makes more sense if this method returns an 
empty array instead of raising when it finds no
ips. This lets the iteration over that array
handle the 0 case, and we can use a conditional on
the len(of the ips) if really needed. I'm not sure
that log is needed to say "No fixed IPs 
deallocated" or if that is an artifact of needing 
something to put in the exception handler.

Change-Id: Ib9f66affb5360fb11a3ab5f415a0e57602cec886

nova/db/api.py

@@ -416,9 +416,9 @@ def fixed_ip_get_by_network_host(context, network_id, host):
     return IMPL.fixed_ip_get_by_network_host(context, network_id, host)
 
 
-def fixed_ip_get_by_virtual_interface(context, vif_id):
+def fixed_ips_by_virtual_interface(context, vif_id):
     """Get fixed ips by virtual interface or raise if none exist."""
-    return IMPL.fixed_ip_get_by_virtual_interface(context, vif_id)
+    return IMPL.fixed_ips_by_virtual_interface(context, vif_id)
 
 
 def fixed_ip_get_network(context, address):

nova/db/sqlalchemy/api.py

@@ -876,15 +876,12 @@ def fixed_ip_get_by_network_host(context, network_id, host):
 
 
 @require_context
-def fixed_ip_get_by_virtual_interface(context, vif_id):
+def fixed_ips_by_virtual_interface(context, vif_id):
     result = model_query(context, models.FixedIp, read_deleted="no").\
                  options(joinedload('floating_ips')).\
                  filter_by(virtual_interface_id=vif_id).\
                  all()
 
-    if not result:
-        raise exception.FixedIpNotFoundForVirtualInterface(vif_id=vif_id)
-
     return result