Fix nova floating-ip-* command failures

This pull request fixes the failures in the 'nova floating-ip-create, nova floating-ip-associate, nova floating-ip-disassociate ..' commands.
Two fixes are required to support these commands
1. nova  calls neutron.get_ports with 'device_owner' set in the 'filters'. 
2. nova calls neutron.get_floatingips with 'floating_ip_address' set in filters. If 'floating_ip_address' is set, then 'floatingip_list' function should return only the list of floating ips with the specified floating_ip_address and not all the floating ips.