Force test:// URI to be used in mocked connections

Prior to 801ce47 any URL could be used
when mocking and it had preconfigured responses, but this regressed and
could cause real system connections to go through.

This forces the URL to use the test:// scheme which still allows the use
of test:///path/to/host/definitions as documented.

Fixes: 801ce47 ("Use test:///default in tests")
Reference: https://libvirt.org/uri.html#test-test-uris

lib/fog/libvirt/compute.rb

@@ -117,6 +117,12 @@ class Real
 
       class Mock
         include Shared
+
+        def enhance_uri(uri)
+          uri = 'test:///default' unless ::URI.parse(uri).scheme == 'test'
+
+          super(uri)
+        end
       end
     end
   end