race: funcLogger write race

[rdallman]

this could be a write-write race when using a func logger as both stdout and stderr, a write-write race when closing a func logger when it may still be writing lines or a write-read race from the same close method with a different configuration.

the symptom is a panic at this line https://github.com/fnproject/fn/blob/master/api/agent/func_logger.go#L154 when calling Next() to advance the inner buffer, the slice bounds is out of range. we need to fix this, logging has been disabled for the oracle functions service so it's good there, but this is still hanging out if configured, mostly because of the log api, which we also need to remove really.