Logging AMI ID

This pull would add in methods to both save and read the registered AMI ID. It also uses those methods to log the AMI ID as the last line of logging output, instead of 'Amination Complete!' This allows for the AMI ID to be more easily machine readable. Here's a bash example that does just that using tail and awk.

```
aminate ....args... 2> stderr.log >stdout.log
LAST_LINE=$(tail -n 1stdout.log)
AMI_ID=$(echo $LAST_LINE | awk '{print substr($0,index($0,"AMI: ")+5)}')
```

Sorry to keep inundating you guys with these requests