Bazel: Add --build_tests_only to test commands per default

When `build test ...` is run, we would like to avoid to build the
whole world.

Change-Id: I9e2c65045ab3c08ab5f78d973ce09dbb4fde7a5c
diff --git a/tools/bazel.rc b/tools/bazel.rc
index 2210511..4ed16cf 100644
--- a/tools/bazel.rc
+++ b/tools/bazel.rc
@@ -1 +1,2 @@
 build --workspace_status_command=./tools/workspace-status.sh
+test --build_tests_only