run-unit-test-docker: add comment for TEST_ONLY

The NO_FORMAT_CODE option is in the comment block. It also makes sense
to add the TEST_ONLY option to that comment block.

Tested: tested locally though it only changes a comment.

Signed-off-by: Nan Zhou <nanzhoumails@gmail.com>
Change-Id: I49f48e813c633bd89b9c82df128e84e3c59c8993
1 file changed