add license header and timeout to cloudbuild.yaml

.kokoro/docker/cloudbuild.yaml

@@ -1,3 +1,19 @@
+# Copyright 2020 Google LLC
+#
+# 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.
+
+timeout: 7200s  # 2 hours
+
 steps:
     - name: 'gcr.io/cloud-builders/docker'
       args: ['build', '-t', 'gcr.io/$PROJECT_ID/python-samples-testing-docker', '.']