feat(docker registry): add Vagrantfile for Docker registry

Adds a contrib/docker-registry directory with a Vagrantfile that
configures and starts a VM with the Docker registry service.
chore(*): rely on etcdctl in deis/base

As of deis/base#4, etcdctl v0.4.2 includes the --no-sync option.
We no longer need to install an etcdctl branch just to get this
option.
Merge pull request #1163 from deis/remove-etcdctl

chore(*): rely on etcdctl in deis/base
chore(builder): rely on deis/base to manage confd

Please test this PR in conjunction with deis/base#3
Merge pull request #1161 from deis/confd-v0.4.1

chore(builder): rely on deis/base to manage confd
fix(docker-registry): up timeout

Slow connections wouldn't pull the image in under 90 seconds.
Merge pull request #1135 from deis/feat-local_registry

feat(docker registry): add Vagrantfile for Docker registry
fix(*): fix etcd_safe_set to not override values

Refactors etcd_safe_set so it doesn't overwrite custom settings.

TESTING: rebuild and restart components, setting a non-default
custom value
```console
dev $ make uninstall
dev $ vagrant rsync && make build
dev $ vagrant ssh
coreos $ etcdctl set /deis/controller/webEnabled 1
dev $ make run
```
Make sure the settings have taken effect.

Changes proposed by @aledbf

fixes #1210