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
Do you forsee a pattern of chaining together handlers that follow this format:
`func DoStepN(context Request, doer StepNDoer, failed http.Handler, handler http.Hander)`
for steps like authentication, authorization, quota checking, REST object read/write, field projection, response compression?

If so, I think I like it.