Make use of types for websocket library

[cjlarose]

This fixes a compilation error I was getting when trying to import this library. The generated exec.d.ts file looked like this:

/// <reference types="node" />
import stream = require('stream');
import { WebSocketHandler } from './web-socket-handler';
import { KubeConfig } from './config';
export declare class Exec {
    'handler': WebSocketHandler;
    constructor(config: KubeConfig);
    exec(namespace: string, podName: string, containerName: string, command: string, stdout: stream.Writable | any, stderr: stream.Writable | any, stdin: stream.Readable | any, tty: boolean): Promise<WebS
ocket>;
}

which produced this error

../../kubernetes-js-client/node-client/dist/exec.d.ts(8,201): error TS2304: Cannot find name 'WebSocket'.

I suspect that these changes also fix an error related to HTTP Basic Auth when using websockets connections because the auth property on the WebSocket connection was being set to an object instead of a ${username}:${password} string as NodeJS's HTTPS client expects.

[brendandburns]

@cjlarose thanks for the PR, I just merged #39 so this needs a rebase, but then I think we can merge this...

[cjlarose]

@brendanburns I think that #39 made a bunch of the same changes as this PR.

One notable difference is that #39 removed the use of this.config.applyToRequest when making a secure WebSockets connection, so some TLS options appear to no longer be passed (ca, cert, key). I don't know if those options are important or not. If they are, I think it's a regression, but regardless, it's a separate issue from this original PR.

[sheldonkwok]

Yeah, I just noticed that as well. I created a new pull request here: #41

Rebasing yours works for me as well.

[cjlarose]

@sheldonkwok I like yours better. Let's go with #41.