use token from command line

This links --token to an existing kube client config option to build a bearer transport for end to end testing and adds BearerToken as one of the fields retrieved from the ~/.kubernetes_auth file.
```
type Config struct {
   MasterAddr flagtypes.Addr
   KubernetesAddr flagtypes.Addr
   ClientConfig client.ClientConfig
}

func BindClientConfig(config *client.ClientConfig, flags) {
	flags.BoolVar(&config.Insecure, "insecure_skip_tls_verify", config.Insecure, "If true, the server's certificate will not be checked for validity. This will make your HTTPS connections insecure.")
	flags.StringVar(&config.CertFile, "client_certificate", config.CertFile, "Path to a client key file for TLS.")
	flags.StringVar(&config.KeyFile, "client-key", config.KeyFile, "Path to a client key file for TLS.")
	flags.StringVar(&config.CAFile, "certificate-authority", config.CAFile, "Path to a cert. file for the certificate authority")
        flags.StringVar(&config.BearerToken, "token", ....)
}

func (c *Config) Bind(flags) {
    // existing binds
    BindClientConfig(&c.Config, flags)
}
```

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