Abstract the error handling for the storage layer to eliminate the

direct etcd dependency.

pkg/master/master.go

@@ -836,6 +836,7 @@ func (m *Master) getServersToValidate(c *Config) map[string]apiserver.Server {
 			addr = etcdUrl.Host
 			port = 4001
 		}
+		// TODO: etcd health checking should be abstracted in the storage tier
 		serversToValidate[fmt.Sprintf("etcd-%d", ix)] = apiserver.Server{Addr: addr, Port: port, Path: "/health", Validate: etcdutil.EtcdHealthCheck}
 	}
 	return serversToValidate