Move client/unversioned/remotecommand to client-go

Module remotecommand originally part of kubernetes/pkg/client/unversioned was moved
to client-go/tools, and will be used as authoritative in kubectl, e2e and other places.

Module remotecommand relies on util/exec module which will be copied to client-go/pkg/util

Kubernetes-commit: 2612e0c78ad18ac87bbd200d547100cf99f36089

tools/remotecommand/errorstream.go

@@ -0,0 +1,55 @@
+/*
+Copyright 2016 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package remotecommand
+
+import (
+	"fmt"
+	"io"
+	"io/ioutil"
+
+	"k8s.io/apimachinery/pkg/util/runtime"
+)
+
+// errorStreamDecoder interprets the data on the error channel and creates a go error object from it.
+type errorStreamDecoder interface {
+	decode(message []byte) error
+}
+
+// watchErrorStream watches the errorStream for remote command error data,
+// decodes it with the given errorStreamDecoder, sends the decoded error (or nil if the remote
+// command exited successfully) to the returned error channel, and closes it.
+// This function returns immediately.
+func watchErrorStream(errorStream io.Reader, d errorStreamDecoder) chan error {
+	errorChan := make(chan error)
+
+	go func() {
+		defer runtime.HandleCrash()
+
+		message, err := ioutil.ReadAll(errorStream)
+		switch {
+		case err != nil && err != io.EOF:
+			errorChan <- fmt.Errorf("error reading from error stream: %s", err)
+		case len(message) > 0:
+			errorChan <- d.decode(message)
+		default:
+			errorChan <- nil
+		}
+		close(errorChan)
+	}()
+
+	return errorChan
+}