Add an empty tools/BUILD file explicitly for Bazel
Add an empty tools/BUILD file explicitly for Bazel

To make sure that all plugins consistently have empty BUILD files
within their tools.

Change-Id: I0197cbfae340df999cc6aaca826802827fd90e44

GerritCodeReview/plugins_delete-project,GerritCodeReview/plugins_delete-project,GerritCodeReview/plugins_delete-project,GerritCodeReview/plugins_delete-project