Unittest for #9762

Started looking at refactoring of the kubectl Factory, which
caused me to experience all 5 stages of grief. There are some options
for improving, but it probably warrants a proposal with some discussion/
feedback. In the meantime this tests `NegotiateVersion` in isolation.

pkg/kubectl/cmd/util/clientcache.go

@@ -36,6 +36,7 @@ type clientCache struct {
 	clients       map[string]*client.Client
 	configs       map[string]*client.Config
 	defaultConfig *client.Config
+	defaultClient *client.Client
 	matchVersion  bool
 }
 
@@ -48,7 +49,7 @@ func (c *clientCache) ClientConfigForVersion(version string) (*client.Config, er
 		}
 		c.defaultConfig = config
 		if c.matchVersion {
-			if err := client.MatchesServerVersion(config); err != nil {
+			if err := client.MatchesServerVersion(c.defaultClient, config); err != nil {
 				return nil, err
 			}
 		}
@@ -58,7 +59,7 @@ func (c *clientCache) ClientConfigForVersion(version string) (*client.Config, er
 	}
 	// TODO: have a better config copy method
 	config := *c.defaultConfig
-	negotiatedVersion, err := client.NegotiateVersion(&config, version)
+	negotiatedVersion, err := client.NegotiateVersion(c.defaultClient, &config, version)
 	if err != nil {
 		return nil, err
 	}