Fix #106

```
% fleetctl submit build/units/subgun.1.service
Creation of payload subgun.1.service failed: 105: Key already exists (/_coreos.com/fleet/payload/subgun.1.service) [2538]
% fleetctl start build/units/subgun.1.service
Creation of job subgun.1.service failed: 105: Key already exists (/_coreos.com/fleet/job/subgun.1.service/object) [2542]
% fleetctl --endpoint=http://127.0.0.2:3001/ start build/units/subgun.1.service
Creation of payload subgun.1.service failed: 501: All the given peers are not reachable (Tried to connect to each peer twice and failed) [0]