fix(*): etcdctl and docker history commands eat error output

These errors are benign, but confusing to new users.

TESTING: reprovision a cluster (due to changes in cloud config), build
components from source, `make run`, and ensure that there are no
confusing errors in the output

```console
$ vagrant destroy -f && vagrant up
$ make build run
```

```
$ fleetctl status deis-router.1
< snipped... >
Jul 23 19:18:53 deis-1 systemd[1]: Starting deis-router...
Jul 23 19:18:54 deis-1 systemd[1]: Started deis-router.
Jul 23 19:19:06 deis-1 sh[4546]: router: waiting for confd to write initial templates...
Jul 23 19:19:11 deis-1 sh[4546]: Starting Nginx...
Jul 23 19:19:11 deis-1 sh[4546]: deis-router running...
```
Merge pull request #1407 from deis/etcdctl_eat_errors

fix(*): etcdctl and docker history commands eat error output