servers api should return security group ids instead of names

Creating this from https://bugs.launchpad.net/python-novaclient/+bug/1394462

In nova-network security group names can't be duplicated, but in neutron, they can. For this reason, it would be nice to return server security groups as ids instead of names.

Here's is a sample request and response showing the current state: "security_groups": [{"name": "default"}],

DEBUG (connectionpool:415) "GET /v2/038c717809174199a297f4ef774e6852/servers/d2b729b8-a626-4050-a756-d5a450c99811 HTTP/1.1" 200 1757
DEBUG (session:223) RESP: [200] date: Mon, 30 Mar 2015 17:57:50 GMT content-length: 1757 content-type: application/json x-compute-request-id: req-d6c33e18-cf62-4848-88ff-e57b64bd55e3
RESP BODY: {"server": {"status": "ACTIVE", "updated": "2015-03-25T19:04:47Z", "hostId": "cfca2250a844c76f4dd5ba369b2550ad3fb07d545e58e395b2271486", "OS-EXT-SRV-ATTR:host": "vagrant-ubuntu-trusty-64.localdomain", "addresses": {"private": [{"OS-EXT-IPS-MAC:mac_addr": "fa:16:3e:0d:0c:b3", "version": 4, "addr": "10.0.0.2", "OS-EXT-IPS:type": "fixed"}]}, "links": [{"href": "http://10.0.2.15:8774/v2/038c717809174199a297f4ef774e6852/servers/d2b729b8-a626-4050-a756-d5a450c99811", "rel": "self"}, {"href": "http://10.0.2.15:8774/038c717809174199a297f4ef774e6852/servers/d2b729b8-a626-4050-a756-d5a450c99811", "rel": "bookmark"}], "key_name": null, "image": {"id": "d0ddfda2-dbdc-48ae-b65e-27ca407d32ce", "links": [{"href": "http://10.0.2.15:8774/038c717809174199a297f4ef774e6852/images/d0ddfda2-dbdc-48ae-b65e-27ca407d32ce", "rel": "bookmark"}]}, "OS-EXT-STS:task_state": null, "OS-EXT-STS:vm_state": "active", "OS-EXT-SRV-ATTR:instance_name": "instance-00000001", "OS-SRV-USG:launched_at": "2015-03-25T19:04:47.000000", "OS-EXT-SRV-ATTR:hypervisor_hostname": "vagrant-ubuntu-trusty-64.localdomain", "flavor": {"id": "42", "links": [{"href": "http://10.0.2.15:8774/038c717809174199a297f4ef774e6852/flavors/42", "rel": "bookmark"}]}, "id": "d2b729b8-a626-4050-a756-d5a450c99811", "security_groups": [{"name": "default"}], "OS-SRV-USG:terminated_at": null, "OS-EXT-AZ:availability_zone": "nova", "user_id": "0771ff29994b428fa15dfb4ec1b6bc7d", "name": "ServerActionsTestJSON-instance-367700261", "created": "2015-03-25T19:04:35Z", "tenant_id": "a0c8d64c558b42d5a7b32a229c9f9a3e", "OS-DCF:diskConfig": "MANUAL", "os-extended-volumes:volumes_attached": [], "accessIPv4": "", "accessIPv6": "", "progress": 0, "OS-EXT-STS:power_state": 1, "config_drive": "True", "metadata": {}}}