redirect apache logs to docker stdout/stderr

[jgangemi]

yesterday i spent quite a bit of time trying to figure out why requests weren't being proxied to the registry properly. i finally figured it out after exposing /var/log/apache2 as a volume and mounting it in another container to tail the logs.

it would be great if the container could do this automatically so one would just need to run docker logs to see the output.

i'd also have no problem with this being controlled via an env variable so it can be toggled on/off.

[kwk]

@jgangemi I've fixed the issue in v2 and v1-deprecated branch. Sorry that it took so long.