Make allowed_sync_hosts option in container-server.conf customizable.

Patch writes a default value for allowed_sync_hosts into container-server.conf (http://docs.openstack.org/folsom/openstack-object-storage/admin/content/container-server-configuration.html) but allows to customize it like 
```ruby
  class { 'swift::storage::container': allowed_sync_hosts => ['127.0.0.1', 'swift01', 'swift02'] }
  class { 'swift::storage::all':
    storage_local_net_ip => $ipaddress_eth1,
  }
```