feat(router): customize health-check route and add SSL redirect

I pulled #2781 and #2782 into the same PR so they'd be easier to test. This also enabled me to refactor the default route for both the healthcheck endpoint and SSL redirect into the same config block, cleaning up the config and ensuring they apply to everything (i.e. before the controller, builder, store-gateway, or app routes are processed). 

TESTING: add an SSL cert, enable SSL redirects, change the custom health-check endpoint, and ensure nothing is broken
You could create another `server` block above. https://github.com/carmstrong/deis/blob/7fd3f6495c6632e69b0d7decb77cd9cd0ba89c66/router/templates/nginx.conf#L154 and use the same server name for http -> https for apps only. Or you move the redirect into a new `server` block (listen  80, but no default_server) directly after the health check. This should redirect all deis components.