Fix#5418
When using a docker logger that doesn't support log streaming through
API, currently docker logger runs a tight loop of Docker API calls
unexpectedly. This change ensures we stop fetching logs early.
Also, this adds some basic backoff strategy when Docker API logging
fails unexpectedly, to avoid accidentally DoSing the docker daemon.
Sometimes the nomad docker_logger may be killed by a service manager
when restarting the client for upgrades or reliability reasons.
Currently if this happens, we leak the users container and try to
reschedule over it.
This commit adds a new step to the recovery process that will spawn a
new docker logger process that will fetch logs from _the current
timestamp_. This is to avoid restarting users tasks because our logging
sidecar has failed.
This commit adds some extra resiliency to the docker logger in the case
of API failure from the docker daemon, by restarting the stream from the
current point in time if the stream returns and the container is still
running.
