make puppet runonce work with --splay 

With puppet 3.4.2 and --test it is not possible to use --splay and --splaylimit. So I changed the parameters for puppet when using runonce from --test to --onetime, --no-daemonize, --show_diff, --verbose (http://docs.puppetlabs.com/references/latest/man/agent.html). This ensures the same behaviour as before without running puppet in background.