Add convenience methods for HTTP requests

[Chris Kiehl]

Currently we use constructs like this:

dependencies.request(options, function(err, response, blockerJSON) {
            if (err || !response || response.statusCode != 200) {
                var error_msg = (err || (response ? ("bad statusCode: " + response.statusCode) : "bad response")) + " from " + options.url;
                logger.error(error_msg);
                callback(error_msg);
            } else {
                var data;
                try {
                    data = JSON.parse(blockerJSON);
                }
                catch (e){
                    return callback(err);
                }
                callback(null, {issues: data.issues});
            }
        });

We could easily extract the error handling and provide methods like requestJSON().

[Iván Loire]

now that we have job dependency injection, this should be easy to implement (work need to be done on lib/job-dependencies/request)

[Iván Loire]

Introduced two convenient methods (JSON and HTML) under the new easyRequest dependency. With tests.

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