This allows much of the read logic to be shared for other things,
especially for the new log driver proposed in
https://github.com/moby/moby/issues/33475
The only logic for reads in the json logger is around decoding log
messages, which gets passed into the log file object.
This also helps with implementing compression as it allows us to
simplify locking strategies.
Signed-off-by: Brian Goff <cpuguy83@gmail.com>
