Redis down fix

This is related to the issue I filed earlier today: https://github.com/balderdashy/sails/issues/2276

If I set the session and socket stores (or one of them) to use Redis as the adapter, and Redis goes down (for whatever reason), sails has an un-handled exception and crashes. It's actually really easy to fix this and make Sails send a 500 while Redis is down, and then when it comes back up, just re-connect.

Steps to reproduce current bug:
1) Make sure you have configured Redis as the session store (and the socket store)
2) sails lift (while redis is running)
3) go to a page on your app, or any route that works - it works
4) now shutdown redis
5) sails has crashed

I ran the tests, and everything seems to work.

Thanks!