Libcloud 386 GCE Load Balancer Support

This adds Load Balancing support for Google Compute Engine.

Since Load Balancer support for GCE is directly part of the GCE API, all of the API calls were added to the existing compute driver.  Then, wrapper methods were added to the Load Balancer driver to make it compatible with the Libcloud Load Balancer API.

In addition, there are some bug fixes and minor improvements.

Note that I'm still working on the test for the "wrapper" methods in the LoadBalancer driver, but tests have been added for all of the actual API calls that were added to the Compute driver.