Fix FIP bulk schema for 'fixed_ip'

Floating ips bulk list API response is below-
{
    "floating_ip_info": [
        {
            "address": "10.10.10.3",
            "instance_uuid": null,
            "fixed_ip": null,
            "interface": "eth0",
            "pool": "nova",
            "project_id": null
        }
    ]
}

This patch adds the missing "fixed_ip" attribute in schema.

Change-Id: I9000b6b3cb40c95bc3d5f0d3e6457ee464f9c029
diff --git a/tempest/api_schema/response/compute/v2/floating_ips.py b/tempest/api_schema/response/compute/v2/floating_ips.py
index def0a78..7250773 100644
--- a/tempest/api_schema/response/compute/v2/floating_ips.py
+++ b/tempest/api_schema/response/compute/v2/floating_ips.py
@@ -146,8 +146,14 @@
                         'instance_uuid': {'type': ['string', 'null']},
                         'interface': {'type': ['string', 'null']},
                         'pool': {'type': ['string', 'null']},
-                        'project_id': {'type': ['string', 'null']}
+                        'project_id': {'type': ['string', 'null']},
+                        'fixed_ip': {
+                            'type': ['string', 'null'],
+                            'format': 'ip-address'
+                        }
                     },
+                    # NOTE: fixed_ip is introduced after JUNO release,
+                    # So it is not defined as 'required'.
                     'required': ['address', 'instance_uuid', 'interface',
                                  'pool', 'project_id']
                 }