VPC_single_instance_in_subnet.py

line 380, 'yum update -y aws-cfn-bootstrap\n',

this is outdated. Here's console dump on centos 6.7 image.

``` bash
[centos@ip-192-168-2-161 ~]$ sudo yum update -y aws-cfn-bootstrap
Loaded plugins: fastestmirror, presto
Setting up Update Process
Loading mirror speeds from cached hostfile
* base: mirror.tngwebhost.com
* epel: mirror.sfo12.us.leaseweb.net
* extras: mirror.san.fastserv.com
* updates: mirror.supremebytes.com
No Match for argument: aws-cfn-bootstrap
No package aws-cfn-bootstrap available.
No Packages marked for Update
```