REMOVED don't read CHECKS from project directory
ADDED support Host header

You can now check a URL with specific Host header, using a relative URL
of the form:

//example.com/about.html
ADDED wait before terminating old container

Give old container 5 seconds to finish processing in-flight requests

Configured with DOKKU_WAIT_TO_RETIRE
Added spaces in checks output
Merge remote-tracking branch 'upstream/master' into mh-sync-upstream