Add e2e testing for websockets

[pass-by-value]

Required Setup

Please make sure that the test runs in an environment with a salt-master and salt-minion installed. Henceforth in this issue the master and minion are assumed to have ids salt-master and salt-minion respectively. We also require salt-api to be installed.

Recommended Testing (Needs to run on rest_cherrypy and rest_tornado)

• Create a secure websocket connection to salt-api's /formatted_events
• Make sure you receive the following

{minions: ['salt-minion']}

• Repeat for Chrome, Safari, Firefox and any other supported browsers

More test cases to follow, feel free to extend!