Solve Heroku R10 boot timeout

This patch forces Jetty to bind to its port early, thus avoiding the common R10 boot timeout errors that plague Grails apps on Heroku. With this patch the Grails app can take all the time it needs to start up; during startup time, requests simply fail with a 404 error, but at least the app starts reliably.

See ticket: https://help.heroku.com/tickets/84969