Deprecate "provider" flag

This is also deprecated on other provider CLI's since it doesn't make sense to specify one.

cmd/virtual-kubelet/commands/root/flag.go

@@ -62,7 +62,12 @@ func installFlags(flags *pflag.FlagSet, c *Opts) {
 	flags.StringVar(&c.KubeNamespace, "namespace", c.KubeNamespace, "kubernetes namespace (default is 'all')")
 	flags.StringVar(&c.NodeName, "nodename", c.NodeName, "kubernetes node name")
 	flags.StringVar(&c.OperatingSystem, "os", c.OperatingSystem, "Operating System (Linux/Windows)")
+	
 	flags.StringVar(&c.Provider, "provider", c.Provider, "cloud provider")
+	if err := flags.MarkDeprecated("provider", "this flag is not used, alibabacloud is the only supported provider"); err != nil {
+		panic(err)
+	}
+	
 	flags.StringVar(&c.ProviderConfigPath, "provider-config", c.ProviderConfigPath, "cloud provider configuration file")
 	flags.StringVar(&c.MetricsAddr, "metrics-addr", c.MetricsAddr, "address to listen for metrics/stats requests")