Enable v1beta3 API via --runtime_config=api/v1beta3 flag

This exposes the proper v1beta3 API endpoint when the user specifies the --runtime_config=api/v1beta3 argument to the apiserver. v1beta3 is still considered experimental and subject to change.

--runtime_config is a map of string keys and values, that can be specified by providing

    --runtime_config=a=b,b=c,d,e

Only the key must be specified, the value can be omitted.

Enables v1beta3 in hack/local-up-cluster.sh and hack/test-cmd.sh

@bgrant0607

Will allow completion of remaining #1519 items
What I meant was that if we're going to predicate registration of the v1beta3 handlers, we should also predicate its inclusion in the list of supported versions reported by the API version handler.