Comment 0 for bug 1317321

There was a comment on https://review.openstack.org/#/c/90583/ to add an extra test case to handle more than 1 ephemeral disk as well as correct a comment in the code to be more accurate. The purpose of this bug is to add the extra test case for _get_instance_block_device_info to test more than 1 ephemeral disk and correct one of the comments in _get_instance_block_device_info.