Update copyright headers.

- Add copyright headers to files that did not already have them
- Update the year to the last year the file was modified in files with
  existing headers.

wa/workloads/mongoperf/__init__.py

@@ -1,3 +1,18 @@
+#    Copyright 2018 ARM Limited
+#
+# 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.
+#
+
 import json
 import os
 from collections import defaultdict