vSphere:Fixed json output error in empty public_addresses

[ikd-work]

At the specific situation which vm has Network Interface and vmware-tools installed the vm and network interface is down in the vm, public_addresses response is below.(vSphereESXi5.0)

:public_addresses=>[{:address=>{:type=>:unavailable, :value=>}}]

A json error occurs when execute "to_json" at this response.

So, I changed "vsphere_driver.rb" to get empty value.

Please Check this change. And, Please merge trunk branch.

Thanks. Daisuke Ikeda (TIS Inc.)