Fixes issues with uchiwa 0.3.2

Previous PR shipped uchiwa 0.3.2 however some new behaviour skipped my attention. Uchiwa uses websockets so we had to get our nginx to upgrade the connection to Websocket when proxying to uchiwa backend. Also uchiwa needs to point to public HTML directory via -p switch.

I have also added uchiwa nginx template into sensu-formula repo as oppose to using nginx-formula one. This allows us to change sensu config by modifying sensu-formula only. Otherwise this will require modifications in both sensu and nginx formulas.