[recipe_modules/test_result] Fix name of file to be explicit.

When using test-results json format the file name was being set
to the base name of the actual file (normally a random string)
instead of full_results.json.

BUG=649762

Change-Id: If741e353c8b317360b633aeb7be04ea0f08d6603
Reviewed-on: https://chromium-review.googlesource.com/409619
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Commit-Queue: Ned Nguyen <nednguyen@google.com>
1 file changed