Delete fixed_ips if it's empty list

If neutronclient gets fixed_ips = [], created port will not get assigned
ip address. In current patch fixed_ips will be deleted from properties,
if it is empty list. So created port always gets assigned ip address.

Change-Id: I8344180b07ffb61019264f44d23aa400aa1ace31
Closes-bug: #1271597
Merge "Delete fixed_ips if it's empty list"