Add Vcloud support back to Fog::Compute

Vcloud does not work with the new cleanup code for generic provider compute support.
Would return:
NameError: uninitialized constant Fog::Compute::Vcloud
	from /usr/local/ruby/lib/ruby/gems/1.9.1/gems/fog-1.10.0/lib/fog/compute.rb:41:in `const_get'
	from /usr/local/ruby/lib/ruby/gems/1.9.1/gems/fog-1.10.0/lib/fog/compute.rb:41:in `new'
Merge pull request #1640 from dJason/patch-2

Add Vcloud support back to Fog::Compute