agent: stop units in goroutine during init

Fix #624
Merge pull request #630 from bcwaldon/624

agent: stop units in goroutine during init
-l is deprecated && long option are more readable

in last doc (http://www.freedesktop.org/software/systemd/man/journalctl.html) we can read : 
> The old options -l/--full are not useful anymore, except to undo --no-full.

with systemd 204-14 that generate this error : 
    invalid option -- 'l'
Merge pull request #633 from tclavier/patch-1

fleetctl journal: -l is deprecated && long options are more readable
registry: remove redundant requests in Machines
Merge pull request #636 from bcwaldon/redundant-machines

registry: remove redundant requests in Machines
bump: update go-systemd deps
Merge pull request #637 from bcwaldon/bump-go-systemd

bump: update go-systemd deps
job: add Job.Scheduled method
engine: switch to reconciler model
engine: refactor reconcile routine
registry: return error from UnresolvedJobOffers
registry: use recursive request in UnresolvedJobOffers