Use ws instead of faye-websocket for websocket tests

[bliuchak]

Currently we have both libraries in our devDependencies. Let's migrate out tests to use ws fully instead of faye-websocket.

Why it makes sense:

• ws is de-facto a standard websocket library for Node
• ws has better maintainability (faye-websocket got last commit 2 years ago)
• ws has better wss support, because of it it's already imported in test/tls_overhead_stats.js
• no new need to introduce new dependency

[tobice]

Nish says that Node.js now has a native Websocket client.