Updated for gcutil-1.8.3 and adding support for GCE load-balancer

This PR contains:
* Updates for latest gcutil-1.8.3
* New types for load-balancer gce_{httphealthcheck,targetpool,forwardingrule} - see GCE docs for more
* Updates to `files/puppet-community.sh` for bootstrapping GCE nodes with custom manifests and side-loading with [External Node Classifiers](http://docs.puppetlabs.com/guides/external_nodes.html)
* Extensive testing with Debian wheezy nodes and puppet-2.7.18 (default on wheezy) and puppet-3.2.3 (latest available on http://apt.puppetlabs.com/debian)
* More examples added to `tests/*.pp`