Verify the attributes of 'set-server-metadata' API

This patch verifies the response attributes of 'set-server-metadata'.
The response attributes of v2 and v3 are the same:
{
    "metadata": {
        "foo": "Foo Value"
    }
}
Partially implements blueprint nova-api-attribute-test

Change-Id: Ifffa537a228819326f00fd0c98271882fb42f8c3
Verify 'list-server-metadata' APIs attributes

This patch verifies the response attributes of 'list-server-metadata'.

The response attributes of v2 and v3 are the same:
{
    "metadata": {
        "foo": "Foo Value"
    }
}

Partially implements blueprint nova-api-attribute-test

Change-Id: Iab1cb1efc0293e8e0aa5124752ec95048b8608bf
Merge "Verify the attributes of 'set-server-metadata' API"
Merge "Verify 'list-server-metadata' APIs attributes"