Adds a configurable wait time to runit scripts

Addresses [COOK-3337](http://tickets.opscode.com/browse/COOK-3377). 

Because unicorn convention is to sleep 1 between forking, and runit has
a 7 second timeout for service start, running >7 unicorn children is
likely to cause a runit timeout.

This adds a new attribute `runit_wait_time` to the `application_ruby`
provider that allows setting the time runit will wait before timing
out. It defaults to 10, instead of runit's default of 7.

It's possible that this should be moved to the runit_service LWRP, but this was the simplest fix at the time, as it only requires 3 lines to address.

Feedback appreciated.