chore(contrib/coreos): upgrade fleet to 0.9.2
chore(contrib/coreos): upgrade fleet to 0.9.2

This commit introduces a systemd unit to upgrade fleet to 0.9.2
before the daemon is started. This is intended to address
https://github.com/coreos/fleet/issues/1158 which was a regression
from fixes introduced in fleet 0.9.1, which is included for the first
time in CoreOS 607.0.0.

deis/workflow,deis/workflow,deis/workflow