Complete net-show/net-list/subnet-list/subnet-show

Clean up and improve the neutron network/subnet list/show response body to make it openstack
compatible.

Change-Id: I0047c14eee758c1a283cdc53757544c45994faf3
This can be handled more elegantly by using object filters.

Example:
```python
_filter = {}
if req.get_param('name'):
    _filter = {'subnets': {'id': {'operation': req.get_param('name')}}}

client['Account'].getSubnets(filter=_filter)
```
Another usage of this for nova server listing: https://github.com/softlayer/jumpgate/blob/master/jumpgate/compute/drivers/sl/servers.py#L246