Refactor handlers to have a DSL

[thheinen]

The current way of declaring default options for request and release in handlers is not very TestKitchen-like. Instead, create a Handler DSL to define this like:

class Script < Base
  handler_type 'script'
  handler_version 1

  request_option :match_hostname, '^(.*)$'
  request_option :match_banner

  release_option :execute_ruby, -> { ... }

  # ...
end

PoC already exists internally.