[Compute|Libvirt] Take into account a query string can be empty, different on some rubies it gives nil, on some empty string

lib/fog/libvirt/models/compute/uri.rb

@@ -126,12 +126,16 @@ module Fog
         # http://libvirt.org/remote.html
         private
         def value(name)
+          unless @parsed_uri.query.nil?
             params=CGI.parse(@parsed_uri.query)
             if params.has_key?(name)
               return params[name].first
             else
               return nil
             end
+          else
+            return nil
+          end
         end