journald logs: drain 1 more time at container exit

[tnozicka]

resurrected #218 (for master) after @ncdc

I hope it fixes openshift/origin#17747

In the journald log driver, attempt to drain the journal 1 more time
after being told to stop following the log. Due to a possible race
condition, sometimes data is written to the journal at almost the same
time the log watch is closed, and depending on the order of operations,
sometimes you miss the last journal entry.

I'm opening this here for starters so we can discuss. If we decide to proceed with this or something like it, I'll open a pull against docker/docker.

Fixes issues seen in OpenShift e2e tests such as this: openshift/origin#9839 (comment)

/cc @nalind @runcom @rhatdan @smarterclayton @mrunalp @jwhonce @soltysh @mfojtik @deads2k

[runcom]

@nalind PTAL

[runcom]

@tnozicka branch is wrong, you need to open this PR against docker-1.12.6 branch

[tnozicka]

oh, that already has it, I guess it just lacked a link in the old PR
https://github.com/projectatomic/docker/blob/docker-1.12.6/daemon/logger/journald/read.go#L262-L269

apologies for the noise