[android] Use contextlib_ext.Optional for conditional context managers.

Scripts in //build/android have been using hand-rolled workarounds for
conditional context managers in the past. This switches them to a new
implementation I added to catapult in
https://codereview.chromium.org/2585763004/

Review-Url: https://codereview.chromium.org/2593903002
Cr-Commit-Position: refs/heads/master@{#440103}
diff --git a/build/android/test_runner.pydeps b/build/android/test_runner.pydeps
index ea43ae8b..2d4200c 100644
--- a/build/android/test_runner.pydeps
+++ b/build/android/test_runner.pydeps
@@ -11,6 +11,7 @@
 ../../third_party/catapult/common/py_utils/py_utils/__init__.py
 ../../third_party/catapult/common/py_utils/py_utils/cloud_storage.py
 ../../third_party/catapult/common/py_utils/py_utils/cloud_storage_global_lock.py
+../../third_party/catapult/common/py_utils/py_utils/contextlib_ext.py
 ../../third_party/catapult/common/py_utils/py_utils/lock.py
 ../../third_party/catapult/dependency_manager/dependency_manager/__init__.py
 ../../third_party/catapult/dependency_manager/dependency_manager/archive_info.py