Add return value of classmethod in network base.py

Add return value for create_router_interface method

Change-Id: Ieeeaf55e71847372452b2c0ed18eea92ddd3e034
Verify quotas attributes through Nova os-quota-sets API

This patch adds checks whether a response of Nova os-quota-sets
get/get defaultAPI
includes the attributes to block the backward incompatibility change
in the future.

The quotas response body of v2 API is the following:
{
    "quota_set": {
        "id": "231a1e7fd1b344f9874d0334d98b459c",
        "instances": 10,
        "cores": 20,
        "ram": 51200,
        "floating_ips": 10,
        "fixed_ips": -1,
        "metadata_items": 128,
        "injected_files": 5,
        "injected_file_content_bytes": 10240,
        "injected_file_path_bytes": 255,
        "key_pairs": 100,
        "security_groups": 10
        "security_group_rules": 20,
    }
}

The one of v3 API is the following:
{
    "quota_set": {
        "id": "231a1e7fd1b344f9874d0334d98b459c",
        "instances": 10,
        "cores": 20,
        "ram": 51200,
        "floating_ips": 10,
        "fixed_ips": -1,
        "metadata_items": 128,
        "key_pairs": 100,
        "security_groups": 10
        "security_group_rules": 20,
    }
}

Partially implements blueprint nova-api-attribute-test

Change-Id: I8a45ba601b92f17808227a4853a42e812a2a082e
Merge "Verify quotas attributes through Nova os-quota-sets API"
Merge "Add return value of classmethod in network base.py"