Procfile: add a proxy

Woo! Now we have a cluster and a proxy and etcdctl works when running
the procfile by default!

Procfile

@@ -2,3 +2,4 @@
 etcd0: ./etcd -id 0x0 -l :8080 -peers '0x0=localhost:8080&0x1=localhost:8081&0x2=localhost:8082'
 etcd1: ./etcd -id 0x1 -l :8081 -peers '0x0=localhost:8080&0x1=localhost:8081&0x2=localhost:8082'
 etcd2: ./etcd -id 0x2 -l :8082 -peers '0x0=localhost:8080&0x1=localhost:8081&0x2=localhost:8082'
+proxy: ./etcd -proxy-mode -l :4001 -peers '0x0=localhost:8080&0x1=localhost:8081&0x2=localhost:8082'