[vsphere] fixed an issue introduced in commit e8630a0 where @service is nil

There appears to have been a bug that made its way in that causes this error when attempting to find a VM by UUID. This change I submitted reverts the specific line to before commit SHA: e8630a00831cc17d61d48af9501773002dccc165 .

NoMethodError: undefined method `searchIndex' for nil:NilClass
	from /Users/mblack/.rvm/gems/ruby-1.9.3-p125/gems/fog-1.8.0/lib/fog/vsphere/requests/compute/get_virtual_machine.rb:15:in `get_vm_ref'
	from /Users/mblack/.rvm/gems/ruby-1.9.3-p125/gems/fog-1.8.0/lib/fog/vsphere/requests/compute/get_virtual_machine.rb:6:in `get_virtual_machine'
	from (irb):5