Change default in listen block to default_server.

Using just default in listen is outdated and should be default_server.
For more see
http://nginx.org/en/docs/http/ngx_http_core_module.html#listen
Merge pull request #20 from puppetlabs-operations/default_server

Change default in listen block to default_server.
Add multi loadbalancer support.

Setup a way to include two loadbalancer classes. the upstream workers is
now workers-${name} and nginx::loadbalancer has support to define if it
is the default vhost.
Merge pull request #21 from puppetlabs-operations/multi_vhost

Add multi loadbalancer support.