validate server action 'console_output' attributes

This patch adds the JSON schema for Nova V2 & V3 get_console_output
server action APIs response and validate the response with added
JSON schema to block the backward incompatibility change in the future.

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

{
        "output": "FAKE CONSOLE OUTPUT\nANOTHER\nLAST LINE"
}

Partially implements blueprint nova-api-attribute-test

Change-Id: I22e61d1fed926aa9a310a46b12748db401dec045
Merge "validate server action 'console_output' attributes"