SSH error logs in beacon do not have timestamps

@robdimsdale @evanshort73 We were trying to correlate errors across multiple concourse components, and noticed that the following beacon errors do not have timestamps.

```
ssh: Could not resolve hostname tsa.service.dc1.consul: Name or service not known
Warning: Permanently added the RSA host key for IP address '[10.0.16.11]:2222' to the list of known hosts.
```
