Adds "add_dhcp_agent" to test_dhcp_agent_scheduler

This submission is to verify add-dhcp-agent-to-network functionality
and also added required support functions in both XML/JSON interfaces.

Change-Id: I6e9f8336db6d72b1123220f792091ca17b1b1647
Check create/delete keypair attribute of Nova APIs

This patch adds the JSON Schema for response of Nova V2 & V3
create & delete keypair APIs and validate the response with
added JSON Schema to block the backward incompatibility change
in the future.

The response body of V2 & V3 create_keypairs APIs is same and
given below:

{
    "keypair": {
        "fingerprint": "%(fingerprint)s",
        "name": "%(keypair_name)s",
        "public_key": "%(public_key)s",
        "user_id": "fake",
        "private_key": "%(private_key)s"
    }
}

Response status code differ for create and delete keypairs

V2 - create_keypair = 200
V2 - delete_keypair = 202
V3 - create_keypair = 201
V3 - delete_keypair = 204

Partially implements blueprint nova-api-attribute-test

Change-Id: I179f0f11a43324d81ecbb41c0eae2f7072e8979a
Merge "Check create/delete keypair attribute of Nova APIs"
Merge "Adds "add_dhcp_agent" to test_dhcp_agent_scheduler"