Reintroduce "Turn the hack/e2e.go commands into standalone scripts."

This reverts commit 2765660101,
which reverted a commit 0c7dce77dd, so
we're reintroducing the same code from that commit here.

hack/e2e-internal/build-release.sh

@@ -0,0 +1,34 @@
+#!/bin/bash
+
+# Copyright 2015 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -o errexit
+set -o nounset
+set -o pipefail
+
+KUBE_ROOT=$(dirname "${BASH_SOURCE}")/../..
+
+: ${KUBE_VERSION_ROOT:=${KUBE_ROOT}}
+: ${KUBECTL:="${KUBE_VERSION_ROOT}/cluster/kubectl.sh"}
+: ${KUBE_CONFIG_FILE:="config-test.sh"}
+
+export KUBECTL KUBE_CONFIG_FILE
+
+source "${KUBE_ROOT}/cluster/kube-env.sh"
+source "${KUBE_VERSION_ROOT}/cluster/${KUBERNETES_PROVIDER}/util.sh"
+
+prepare-e2e
+
+test-build-release