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
Why is this a Token rather than a TokenChecker?  It takes a token as an argument.