add systemd root

You're going to wait to use something like uuidgen here, and to use notrunc.

I'd suggest replacing this entire script with this:

```
#!/bin/bash

docker build -t agent .

OUTPUT_FILE=rackspace-monitoring-agent-root.tar.gz
# Create a UUID to identify the build
CONTAINER_UUID=`uuidgen`


docker run agent echo $CONTAINER_UUID
CONTAINER=`docker ps -a --no-trunc |grep $CONTAINER_UUID|awk '{print $1}'|head -n1`
echo $CONTAINER
docker export $CONTAINER | gzip > ${OUTPUT_FILE}
docker rm $CONTAINER
``

This is better in two ways:
 - Uses a UUID so even multiple builds should not race
 - Doesn't keep the container running the whole time when you export.