Update path to buildbox-agent

`buildbox-agent` is now under `/usr/local/bin` ... this task was failing with:

```
TASK: [wolfeidau.buildbox | Register the current buildbox-agent version (if any)] ***
failed: [bb-agent] => {"cmd": "/usr/bin/buildbox-agent -version", "failed": true, "rc": 2}
msg: [Errno 2] No such file or directory
...ignoring
```