use kube::util::find-binary to find kubectl

To centralize binary selection in k/k. Also drop the e2e.test copying
which is no longer needed according to the comment.

hack/ci/e2e-k8s.sh

@@ -71,12 +71,8 @@ build_with_bazel() {
   bazel shutdown || true
   pkill ^bazel || true
 
-  # ensure the e2e script will find our binaries ...
-  # https://github.com/kubernetes/kubernetes/issues/68306
-  # TODO: remove this, it was fixed in 1.13+
-  mkdir -p '_output/bin/'
-  cp 'bazel-bin/test/e2e/e2e.test' '_output/bin/'
-  PATH="$(dirname "$(find "${PWD}/bazel-bin/" -name kubectl -type f)"):${PATH}"
+  local -r kubectl_path="$(source hack/lib/util.sh; kube::util::find-binary '.test')" '_output/bin/'
+  PATH="$(dirname "\""${kubectl_path}"\""):${PATH}"
   export PATH
 }