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.
> I would recommend using ClientConfig directly, and implementing a Bind method that is equivalent to BindClientConfigFlags in Kubernetes pkg/client/flags but that uses our conventions for flag names.

It doesn't actually come out as clean.  We want two distinct configs (different .Host), but we want to many things shared (BearerToken, ClientCert, CAs, etc).  And we want to sometimes override kConfig values with osConfig values if they didn't set the kConfig values.

The first problem with binding directly to the kclient.Config object is that Host is a string and so we don't get the .Provided feedback we get from flagtypes.Addr.  That makes the defaulting impossible.  

The second problem is that flags can only be bound to one variable, so I can only wire --token up to one of the kclient.Config objects.  Since we want common values and we don't want anyone repeating themselves, we can't bind directly to the client we want.

Problem 1 can be overcome by setting up separate host fields and copying the values into the kclient.Config.   Problem 2 can be overcome by setting a common BearerToken somewhere and copying it to two different kclient.Configs.  Doing those things make the code do essentially the same thing is does today, only it looks uglier if you try to start copying and overwriting particular pieces of the kclient.Config.