support encrypted replication

[alexnauda]

I'd like to consider using this image to replicate across data centers, or in other scenarios where the security of the network is not entirely guaranteed. (For example, across availability zones or regions of EC2 classic.) To do this, I think this image would have to support:

• Some way to pass certs into the container, such as a VOLUME in the Dockerfile
• Passing additional options to etcdctl (if etcdctl > 2.0) or using curl in place of etcdctl (if etcdctl < 2.0) (see https://github.com/coreos/etcd/pull/1639)
• Configuring Galera to use encryption, e.g. http://www.percona.com/blog/2013/05/03/percona-xtradb-cluster-for-mysql-and-encrypted-galera-replication/

Is anyone else interested in this?