Add preempt_delay option and fix some typos

* Add preempt_delay option in vrrp_instance section

* fix typo in resources/vrrp.rb (noprempt => nopreempt)

* fix typo in templates/default/script_generic.conf.erb (%<= @interval %> => <%= @interval %>)

* fix error in README.md (:auth_type => 'pass')