etcd cluster integration test

[stellarspot]

This is a request to add etcd integration test which tests several etcd instances:

1. Run 3 etcd servers
2. Wrire/Read data from the etcd cluster
3. Close one server
4. Wrire/Read data from the etcd cluster should succeed
5. Close one more server
6. Wrire/Read data should fail because there is no quorum