code: def cmd_rollback(context):
    
    last_stable = get_versions(context, return_stable=True)
    if len(last_stable) != 1:
      fail("Didn't find a version marked stable for key: {} in env/service: {}/{}".format(
           context.key, context.env, context.service_name))
    context.value = last_stable[0].value
    context.commit_hash = last_stable[0].commit_hash
    context.build_number = last_stable[0].build_number
    context.location = last_stable[0].location
    context.stable = True
    cmd_set(context)
docs: Roll back by finding the most recent "stable" tagged version, and putting it again, so that
    it's the new "current" version.
    Args:
      context: a populated EFVersionContext object