Add simple Bearer authenticator filter for Kube

Now with 100% more implementation. Step 1 of implementing #1430.  Sourced from https://github.com/smarterclayton/origin/commit/b3ccda08e51a4b129348244e7b6c03ccc54750f3

@erictune
I guess authenticator.Token is like cipher.Block.  You have to reverse the package and interface names to get a good name.  I don't like it at all, but I guess it is the Go way.  So, I guess leave it.