Enhance `registry-client/get-features` to handle bad feature requests.

[last-ent]

Right now if we run
(pazuzu.registry-client/get-features "url" [<non-existent-feature>]

It gives an error as such -

Exception in thread "main" clojure.lang.ExceptionInfo: clj-http: status 400 
{: status 400,: headers {
        "Date"
        "Thu, 12 May 2016 12:54:42 GMT", "X-Application-Context"
        "application:dev", "Content-Type"
        "application/json; charset=UTF-8", "Connection"
        "close", "Server"
        "Jetty(9.2.15.v20160210)"
    },: body "{\"code\":\"feature_not_found\",\"message\":\"Feature was not found\",\"detailed_message\":null}",
      : request - time 150,: trace - redirects["http://localhost:8080/api/features"],
      : orig - content - encoding nil
}
, compiling:(/private/var/folders/x6/k3r4p5bs1rjgq2n_yw9qnlhdmt8g0k/T/form-init6583773690946275900.clj:1:125)

[mikkeloscar]

Made obsolete by the switch to Golang CLI.