Fix property_name deprecation when running chef-13
Fix property_name deprecation when running chef-13

The varnish_config resource was using the property name inside of the
actions, which is deprecated:
- https://docs.chef.io/deprecations_namespace_collisions.html

This commit just renames it to new_resource.malloc_size, which
converges successfully in chef-client 13

gusrc/varnish,gsreynolds/varnish,gusrc/varnish,gsreynolds/varnish,rackspace-cookbooks/varnish,gusrc/varnish,rackspace-cookbooks/varnish,rackspace-cookbooks/varnish