Speed up hack/local-up-cluster.sh by manually checking if etcd is ready

Use curl to check if etcd is ready, speeding up startup time of hack/local-up-cluster.sh from >5s to under 1s. If curl is unavailable, revert to the old behavior of waiting 5 seconds. Happy to refactor this in any way if there's a way to make it cleaner.
maybe [ -z "$(which curl)" ]  instead?  I've always seen that more in shell.