I don't think this `start` call can happen inside of the `add-*-handler` functions any longer; there was a recent change: https://github.com/puppetlabs/trapperkeeper-webserver-jetty9/commit/1726ea21062e9508e2b7619f71309190d925853f

which separates the jetty initialization into two trapperkeeper phases (`init` and `start`).  The server itself doesn't get started until the `start` phase, but users can call the `add-*-handler` functions during the `init` phase.  If we try to call `start-context-handler` before the server is actually started, I'm pretty sure that we'd get an error.

I think we probably need a test or two for this new `add-context-handler` function anyway, so it might be good to write one where we call it from `init` and see that it fails, and then update this implementation such that it's compatible with the new organization of the lifecycle phases.

I *believe* that in jetty9, the server automatically calls `start` on the handlers anyway, so it may be that we don't even need to explicitly call `start` on them?