Packer start-runner.sh wrapper script references the old install location

More work to do on the packer image, looks like it's another bug from moving the install location to `/opt`

```
sh-4.2$ cat /var/log/runner-startup.log
/var/lib/cloud/scripts/per-boot/start-runner.sh: line 4: cd: /home/ec2-user/actions-runner: No such file or directory
sh-4.2$
```