Add support to handle HTTP response status codes

[thomaslaurenson]

Example:

[09:16:52.098] >>> Narcing on HTTP request...
127.0.0.1:47392: GET https://keystone.rc.nectar.org.au:5000/v3/projects/Auckland-Security
              << 404 NOT FOUND 98b

This results in the following entry, which is not needed:

    {
        "service": "identity",
        "method": "GET",
        "path": "/v3/projects/Auckland-Security"
    },

Might need to test this, because what happens when the first lookup is access denied. Does it go straight to the next lookup?