registry: return error from DestroyJob
bump: github.com/coreos/go-sytemd/*
registry: use unitModel for Unit serialization
job: drop unused method IsOneshot
api: use "schema" as schema name

This makes the schema generator create the schema file
with the correct package name.
fleetctl: communicate unit destruction failures

Fix #709
docs: update unit files
fleetctl: raise default request timeout to 3s

Fix #743
Merge pull request #736 from robszumski/master

fix(docs): update unit files
event: only trigger engine on Job targetstate changes
Merge pull request #741 from bcwaldon/API-units-pre

Uncontroversial prep code from #730
Merge pull request #748 from bcwaldon/743

fleetctl: raise default request timeout to 3s
Merge pull request #732 from bcwaldon/709

Communicate job destruction failures
registry: add States to retrieve all unit states
event: trigger agent on target and target state changes
Merge pull request #742 from jonboulle/742

fleet engine constantly running
version: bump to v0.6.2+git
registry: add error to States() call
Merge pull request #749 from jonboulle/states

registry: add States to retrieve all unit states
engine: collapse Reconciler and dumbReconciler