Add etcd to swarm

[subfuzion]

Closes https://github.com/appcelerator/amp-project/issues/330

This PR adds etcd to the swarm script.

Verification:

$ docker run --rm --net=host -e ETCDCTL_API=3 quay.io/coreos/etcd:v3.0.4 etcdctl put foo bar
OK
$ docker run --rm --net=host -e ETCDCTL_API=3 quay.io/coreos/etcd:v3.0.4 etcdctl get foo
bar

[freignat91]

it's ok, but it misses
--label amp.swarm="infrastructure"
for etct, otherwise the remove function won't remove it

[subfuzion]

Thanks, good catch!

[subfuzion]

How ironic for me to forget that. Ok, label is added.

[freignat91]

tests ok