Allow values to be hashes at prepend,append,custom cfg for locations

Some times you need to add the same parameter many times ( for example add_header or proxy_set_header) at location scope.

This workaround allow use hashes for this purpose

For example:

nginx::nginx_locations:
  'location_name':
    vhost: example.com
    location: /
    proxy: "http://unicorn"
    location_cfg_append:
      proxy_set_header:
        Host: '"$host"'
        X-Forwarded-For: '"$proxy_add_x_forwarded_for"'