handle dynamic cluster discovery

[hazim1093]

1. Find out how cluster discovery is handled by dockerage/etcd-aws-cluster image.
2. If still required, add functionality to dynamically replace discovery URL each time make runs

[rasheedamir]

@hazim1093 this is what I read:

You must supply a fresh token for every new cluster. This includes when you have to rebuild the cluster using nodes that may have the same IP address. The etcd instances will be confused by this and will not function correctly to build the cluster if you reuse the discovery address.