feat(tail) add a tail command to follow logs

[Tieske]

implements standard 'tail -F ' but waits for (max) 2 minutes initially for the file to appear.

The default file is './servroot/logs/error.log'.

[eskerda]

LGTM, although, since images default to logs on stdout/stderr (do they?), same could be docker-compose logs -f kong right?

[kidd]

with @eskerda's suggestion, access.log is also logged (which might be useful for non-erroring situations)

[Tieske]

standard images do stdout/stderr but the testing framework will override this and set teh prefix to ./servroot and send the files there

Let's leave it at this now, might include access.log later, since that is more complicated as we have to wait for 2 files to appear.

[eskerda]

Creating the files instead of waiting for them might be an option too https://github.com/Kong/kong-gojira/blob/72cd4aaebf461983ef1a858df3a23cda0bc41c00/docker/follow-log.sh#L3-L7