Ability to work with client certificates

[zglozman]

Right now in the request method the cert, key, and ca attribues are not copied. In general it would be good to have control of the entitre options object, for agent setting proxies, etc. Let me know if u want to take care of it yourself or a via pull request

let reqOpts = { url: baseUri.replace(//$/, '') + template(path, options.uriParameters), json: !Buffer.isBuffer(options.body), method, headers, formData: options.formData, body: options.body, qs: options.query, options: options.options, resolveWithFullResponse: true };